First general release of ESP8266 port, and support for frozen bytecode

This release marks the first general release of official ESP8266 support
within the MicroPython code base.  The ESP8266 port has many improvements
and additions, including: websocket and webrepl modules, deep-sleep mode,
reading on UART, enhanced I2C support, enhanced network configuration,
full sequence of start-up scripts (built-in, and, improved filesystem support with automatic flash-size detection
as well as documentation and a tutorial.

Known issues with ESP8266 port are:
- Basic SSL support is available but it works only with relatively short
  data lengths (a few kilobytes).
- WebREPL over SSL is not supported.
- Only 5 or so WebREPL sessions in succession can be started (including
  file transfer sessions), after that the board requires a hard reset.
- File transfer over WebREPL has issues with large files (above a few
  tens of kilobytes).
- By design, only one concurrent WebREPL connection is supported.
- Soft reset doesn't reset the network stack.

In addition to ESP8266 support, this release brings frozen bytecode
which allows to compile bytecode offline and link it into the firmware,
completely eliminating the need for compilation (and the associated
RAM usage) at runtime.  Basic async/await syntax is now supported, and
qstrs are now auto-generated in the build system.

A detailed list of changes is given below.

- explicitly point to required dependencies section
- promote "docs" and "tests" to "major components"
- mention support "async" keyword from Python 3.5

- add list of 842 backers from the ESP8266 campaign

py core:
- modbuiltins: add comment about setting "_" special var
- add async/await/async for/async with syntax
- fix constant folding and inline-asm to work with new async grammar
- emitglue: move typedef of mp_raw_code_t from .c to .h file
- emitglue: make mp_raw_code_t* arguments constant pointers
- makeqstrdata: factor out some code to functions that can be reused
- add ability to have frozen persistent bytecode from .mpy files
- makeqstrdata: add more names for escaped chars and esc non-printable
- simplify "and" action within parser by making ident-rules explicit
- makeqstrdata: fix rendering of qstrs that have non-printable ASCII
- makeqstrdata: add special case to handle \n qstr
- declare help, input, open builtins in core
- map: change hash-table allocation policy to be less aggressive
- makeqstrdefs: add script to automate extraction of qstr from sources
- frozenmod: pass the source name of the frozen module to the lexer
- rework QSTR extraction to work in simple and obvious way
- divide "split" and "cat" phases of qstr extraction for better efficiency
- fix bug passing a string as a keyword arg in a dict
- move call_function_*_protected() functions to py/ for reuse
- windows compatibility
- obj.h: when constructing a small-int cast to mp_uint_t for bit-shift
- emitnative: use MP_OBJ_NEW_SMALL_INT instead of manual bit shifting
- vm: "yield from" didn't handle MP_OBJ_STOP_ITERATION optimization
- modio: rename module name to "uio" for consistency with other modules
- modcollections: rename module name have "u" prefix for consistency

- add initial framebuf module
- add generic machine.I2C class, with bit-bang I2C
- machine_i2c: fix I2C reading by sending ack/nack at end of byte
- machine_i2c: implement I2C memory reading/writing
- moduos_dupterm: don't swallow exceptions in dupterm's read()/write()
- modlwip: lwip_tcp_receive(): Properly handle EOF for non-blocking sock
- modlwip: more debug messages for various edge conditions
- fsusermount: in mount/mkfs, deregister VFS object on error
- modlwip: lwip_tcp_send(): full error handling
- modlwip: lwip_tcp_receive(): full error handling
- modlwip: add ability to run callback on "recv" and "accept" events
- machine_i2c: allow mp_hal_pin_obj_t to be any type, not a ptr
- modlwip: protect recv/accept Python callback against exceptions
- modlwip: workaround esp8266 sendto issue where 1 is returned
- modlwip: add print_pcbs() debug function
- modwebsocket: handle CLOSE control frame
- modussl: throw Python exceptions in case of errors
- modussl: support server-side SSL sockets
- modussl: SSL_OK from ssl_read() means "no user data so far"
- modwebrepl: module to handle WebREPL protocol
- modwebrepl: initial implementation of "get file" operation
- modwebrepl: keep reading data when there's something to read
- modwebrepl: GET_FILE: Send length-prefix chunk with one write()
- modwebrepl: add rate-limiting workaround for broken network drivers
- modwebrepl: set debugging by default to off
- modwebrepl: add support for password
- modlwip: implement sendall() method for TCP sockets
- fix typo of macro that detects if float is enabled

- utils/printf: rework overriding printer of DEBUG_printf()
- utils/pyexec: condition-out GC calls from pyexec
- utils/pyhelp: extract implementation of help(obj) to a library function
- axtls: update to the latest upstream, fix reported MacOSX build issue

- add SSD1306 OLED driver, with I2C and SPI interfaces

- new tool to work with .mpy files; currently it can freeze them
- add support for Python 2.7

- add 6 tests for async await/for/with
- add .exp files for async tests, so they can run with Python 3.4
- fix so it doesn't rely on the order of dict elems
- extmod: move split-on-empty-match tests to a separate test file
- add testcase for yielding from a stopped generator
- run-bench-tests: process tests in alphabetical order
- update for _io/_collections module having been renamed

minimal port:
- add example of frozen persistent bytecode (.mpy file)
- disable async/await syntax

unix port:
- build with MICROPY_PY_UHASHLIB_SHA1 if already building with axTLS
- make sure build dir exists before accessing it for freezing upip
- Makefile: make install more compatible (BSD, etc.)

windows port:
- msvc: implement automatic qstr generation using makeqstrdefs

stmhal port:
- implement basic C-level pin HAL
- use new generic I2C object in machine module
- enable framebuf module
- properly handle RTS/CTS flow control for buf/unbuf transfers
- add Makefile option FROZEN_MPY_DIR to support frozen bytecode
- for frozen bytecode generation, add dependency of qstr file
- l4: add CMSIS files to support STM32L476
- l4: add basic STM32L4xx HAL files
- l4: adapt UART HAL to avoid 64-bit integer division
- update HALCOMMITS due to change to hal
- l4: add board definition files for STM32L476DISC
- l4: add line to Makefile for building L4 series
- l4: modify adc.c to add support for STM32L4 series
- l4: modify uart.c to support L4 MCU
- l4: modify usbd_conf.c to support L4 MCU
- l4: modify rtc.c to support L4 MCU
- l4: modify timer.c to support L4 MCU
- fix machine.unique_id() function to work for all MCUs
- l4: modify mphalport to support L4 MCU
- l4: modify flash.c and storage.c to support L4 MCU
- l4: add support for external interrupts/events
- accel: raise an exception if the accel couldn't be initialised
- use pyhelp_print_obj function
- change i2c.scan() method to scan addresses 0x08-0x77
- fix typo of macro that detects if float is enabled

cc3200 port:
- use pyhelp_print_obj function
- change i2c.scan() method to scan addresses 0x08-0x77
- disable async/await syntax

esp8266 port:
- enable websocket module
- modnetwork: .config(): Check interface whose config is requested
- modnetwork: .config(): Add "authmode" param
- modnetwork: .config(): Add "password" param (W/O)
- add Python modules for initial configuration
- scripts/ set WPA/WPA2 AP mode with a predefined password
- protect modpyb.h header file from multiple inclusions
- implement basic C-level pin HAL
- switch from using custom I2C driver to generic extmod one
- enable framebuf module
- in callback helpers, pop nlr_buf on successful call
- esp_mphal: don't swallow exceptions in dupterm's read()/write()
- esp_mphal: call_dupterm_read(): Fix order of deactivating on EOF
- remove pin_id field from C pin object
- add dummy entries for non-existing pins to simplify pin logic
- add hard IRQ callbacks for pin change on GPIO0-15
- separate 1-wire timing funcs from Python module to save iRAM
- switch integer arith routines to BootROM
- scripts/ module to collect diagnostic info
- enable input() builtin
- scripts/_boot: mount block device on "" instead of "/"
- moduos: add uos.mkdir function
- modmachine: add reset_cause() function
- adapt port to use new auto-qstr generation
- moduos: add dupterm_notify() function
- esp_mphal: protect dupterm_task_handler() from recursive exec
- update feature list for current state of affairs
- modesp: allow esp.deepsleep to take 2nd arg for RF wake opt
- scripts/flashbdev: use all available space in 1MB FlashROM for FS
- modesp: add flash_size() function
- scripts: don't try to create filesystem on 512KB devices or less
- modnetwork: .config(): Add "channel" param
- scripts/flashbdev: disable debug output/checks
- scripts/_boot: print notice when initial setup is executed
- scripts/flashbdev: correct bootloader flash size to match real size
- modnetwork: .config(): Add "hidden ESSID" param
- implement basic deep-sleep capabilities
- add uart_rx_wait and uart_rx_char functions
- implement functionality
- uart: remove obsolete UART rx buffering code
- esp_mphal: remove mp_hal_feed_watchdog
- convert mp_hal_pin_obj_t from pin ptr to simple integer
- allow GPIO16 to be used as a pin in the uPy pin HAL
- change software SPI driver to use general pin HAL
- scripts/websocket_helper: module encapsulating handshake sequences
- scripts/websocket_helper: disable debug output
- scripts/webrepl: webREPL based on C-level websocket object
- scripts/webrepl: convert to persistent daemon
- scripts/webrepl: don't start on import
- scripts/webrepl: allow to override port
- scripts/webrepl: print connection address
- scripts/webrepl: print client address for incoming connections
- scripts/flashbdev: use all available Flash for filesystem
- scripts/webrepl: add "ws://" to "daemon started at" message
- Makefile: add target to build axTLS
- esp8266.ld: put axTLS to FlashROM
- Makefile: override abort() when building axtls
- axtls_helpers: helper/wrapper functions for axTLS
- tests/ don't run test on import
- Makefile: support linking with axTLS built from source
- Makefile: enable "ussl" module; axTLS should be built first using "make axtls"
- move function to esp module and remove pyb module
- move, drivers from tests/ to scripts/
- scripts/ simplify and improve 1-wire driver
- scripts/ remove test function from neopixel driver
- set suitable values for axtls's RT_MAX_PLAIN_LENGTH & RT_EXTRA
- README: add recently required step of 'make axtls'
- modnetwork: make WLAN.ifconfig() read/write
- help: implement help() builtin
- help: add cheatsheet for basic WiFi configuration
- enable WebREPL file transfer rate limiting
- enable webrepl module
- scripts: move all of initial setup to inisetup module
- scripts/inisetup: create default in filesystem
- scripts/webrepl: connection ack prompt is now printed by modwebrepl
- scripts/webrepl: switch to using _webrepl object wrapper
- scripts/webrepl: add "first connection" mode to setup password
- README: mention WebREPL
- Makefile: be sure to pass cross-compiling AR when building axtls
- scripts/webrepl_setup: reject too short passwords
- change platform name from ESP8266 to esp8266
- modnetwork: remove deprecated wifi_mode()
- esp_mphal: add ets_esf_free_bufs(), etc. functions
- modesp: add esf_free_bufs() debugging function
- modesp: add malloc() and free() functions
- scripts/inisetup: enable WebREPL auto-start on boot
- modnetwork: remove .mac() method, move to .config("mac")
- scripts/inisetup: update for nic.mac() method being gone
- scripts/ swap red and green in pixel accessor
- modpybpin: use enum+array instead of struct for parsing args
- modpybpin: use None instead of PULL_NONE for no-pull config
- modpybpin: make pin.irq() methods take keyword args
- tutorial: mention that esptool is available via pip
- scripts/ntptime: add simple NTP client

- esp: enumerate flash access functions
- machine: start to update for esp8266 port
- speed_python: clarify/generalize "Buffers" subsection
- speed_python: generalize "Floating point" subsection
- speed_python: add many more details on memoryviews
- machine: reset_cause() has been implemented for esp8266
- topindex.html: esp8266: Enable quickref/general on the main page
- esp8266/general: start "General information" for esp8266
- esp8266: add info about using deep-sleep mode to quickref
- esp8266/tutorial: add tutorial placeholder page
- ustruct: there's no complete "struct" module, only "ustruct" subset
- esp8266: include usocket module reference
- library/usocket: add link to CPython's socket module
- usocket: socket-specific exceptions are for WiPy only
- usocket: socket.IPPROTO_SEC is WiPy-specific
- usocket: describe address format once at the beginning
- network: esp8266: scan(): add note that bssid is bytes object
- library: group MicroPython-specific modules under separate heading
- library/index: move WiPy "micro-libraries" under corresponding heading
- library/index: esp8266 has the same set of stdlibs as pyboard/unix
- module "time" is actually "utime"
- library/index: make single section for "micro-ified" modules
- library/index: order sections from the most to least standard modules
- Makefile: default BUILDDIR based on MICROPY_PORT
- library: "os" module is actually "uos"
- fix uos and utime heading underlines to be the correct length
- library/utime: add more time functions for unix and esp8266 ports
- utime: describe time() peculiarities in MicroPython
- utime: describe sleep() peculiarities in MicroPython
- library: consistently use admonitions for CPython differences
- ubinascii: clean up grammar
- network: esp8266: Add wlan.ifconfig() method
- network: esp8266: Describe wlan.config() method
- make the short port names in the port/version sidebar lowercase
- esp8266: update quickref to reflect changes to 1-wire and NeoPixel
- library/utime: elaborate on epochs and calendar time maintenance
- esp8266/quickref: add info about WebREPL
- ustruct: document pack_into(), unpack_from()
- sys: document sys.modules
- ustruct: fix argument formatting
- sys: remove port-specific details from description of stdin/out/err
- sys: clarify description of sys.exit()
- sys: clean up print_exception() description
- sys: describe sys.implementation
- sys: describe sys.maxsize
- sys: describe sys.platform is port-neutral manner
- add _collections module reference
- add _io module reference
- _io and _collections were renamed to have standard "u" prefix
- library/machine.I2C: update to reflect ESP8266 implementation
- esp8266/general: webREPL is described in quickref for now
- esp8266/general: add more points to "Multitude of boards" section
- esp8266/general: fix list formatting
- esp8266/general: add techspec section
- esp8266/general: add "Boot process" section
- esp8266_contents: reference general and tutorial docs
- network: esp8266: MAC address is set via .config() method
- esp8266: add ESP8266 tutorial
- machine: generalize docs from just WiPy to other ports
- machine: move WiPy-specific hardware details to its general reference
- machine: more generic description of sleep's, WiPy details to its genref
- machine: idle() description generalization
- library/machine.Pin: update pin docs to reflect ESP8266 support
- esp8266/tutorial: update pins tutorial to reflect changes in API

- add HTTPS server example
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