Update README to current state of affairs.

1. Invite x86 (32-bit) users.
2. Update interpreter name.
3. Update dependency install instructions.
Merge pull request #302 from pfalcon/readme-update

Update README to current state of affairs.
Merge pull request #303 from dhylands/fix-netduino-disc

Fix build for netduino and stm32f4disc
Fix usart_obj_tx_char
stm: Initialize sys.path with ["0:/", "0:/src", "0:/lib"].

This is compatible with what search path was before sys.path refactor,
with addition of module library path ("0:/lib").
Merge pull request #307 from iabdalkader/master

Fix usart_obj_tx_char
Merge pull request #309 from pfalcon/stm-sys-path

stm: Initialize sys.path with ["0:/", "0:/src", "0:/lib"].
objint_longlong: Don't assert on invalid syntax, raise SyntaxError instead.
stm: Implement mp_import_stat.

To follow up pull request #309.
Add pin mapping code.

This commit also introduces board directories and moves board
specific config into the appropriate board directory.

boards/stm32f4xx-af.csv was extracted from the STM32F4xx datasheet
and hand-tweaked.

make-pins.py takes boards/stm32f4xx-af.csv, boards/stm32f4xx-prefix.c,
and boards/BOARD-NAME/pins.csv as input and generates the file
build/pins_BOARD_NAME.c

The generated pin file for PYBOARD4 looks like this:
https://gist.github.com/dhylands/9063231

The generated pins file includes all of the supported alternate
functions, and includes upsupported alternate functions as comments.

See the commnet block at the top of stm/pin_map.c for details on
how to use the pin mapper.

I also went ahead and modified stm/gpio.c to use the pin mapper.