Micro Python port to ESP8266

This is a port of Micro Python to the Espressif ESP8266 wifi module.

Currently implemented features include:

- REPL (Python prompt) over UART0.

- 24k heap RAM available for Python code.

- Garbage collector, exceptions.

- Unicode support.

- Builtin modules: gc, array, collections, io, struct, sys.

- C long-long type used as bignum implementation (gives 64 signed ints).

Note that floating-point numbers are not supported.

On the TODO list:

- Wifi support.

- GPIO support.

- Internal filesystem using the flash.

- ...

Build instructions

The tool chain required for the build is the OpenSource ESP SDK, which can be

found at <https://github.com/pfalcon/esp-open-sdk>. Clone this repository and

run `make` in it's directory to build and install the SDK locally. T

Then, to build Micro Python for the ESP8266, just run:

$ make

This should produce binary images in the `build/` subdirectory. To flash them

to your ESP8266, use:

$ make deploy

This will use the `esptool.py` script to download the images. You must have

your ESP module in the bootloader, and connected to a serial port on your PC.

The default serial port is `/dev/ttyACM0`. To specify another, use, eg:

$ make PORT=/dev/ttyUSB0 deploy

The images that are built are:

- `firmware.elf-0x00000.bin`: to be flashed at 0x00000

- `firmware.elf-0x10000.bin`: to be flashed at 0x10000

There is also a combined image, made up of the above 2 binary files with the

appropriate padding:

- `firmware-combined.bin`: to be flashed at 0x00000