mpconfigport.h is now included by stm32f4xx.h so that all STM files have
access to these defines.

Can now have null bytes in strings.  Can define ROM qstrs per port using
qstrdefsport.h

* Add the option to pass OSC frequency on command line.

CMSIS V3.01 -> V3.20. Now in stm/cmsis to keep separate from ST
libraries.

Thanks to Dave Hylands for this.

* Add simple ADC driver, with support for ADC1 and all channels.
* Export MicroPython ADC object with read_channel function.
* Add stm32f4xx_adc.c and adc.c to Makefile.

See pyb_usart_global_debug variable.

Also did some work on USB OTG, but nothing working yet.

* Add a DEBUG flag to Makefile, enables: "-O0 -ggdb"

Use make V=1e make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.

This should fix issue #117

While updating the teensy Makfile, I noticed that the stm Makefile
was using calling arm-none-eabi-objcopy and size rather than
$(OBJCOPY) and $(SIZE), so I added these 2 for consistency.

Updated mconfigport.h to enable GC

* Add a TARGET definition to Makefile (default PYBOARD).
* Add support for discovery LEDs in led module.
* Add support for discovery user switch in usersw
* Add EXTI interrupt handler for discovery user switch on (PA0).
* Parameterize led and usrsw modules pins and port.
* Issue #83

* Move user switch code from main.c into a separate module (usrsw)
* Add usrsw.c to Makefile

Now much more inline with how CPython does types.

So far, only start and stop integer indexes are supported. Step is
not supported, as well as objects of arbitrary types.

mpconfig.h will automatically pull mpconfigport.h.

import works for simple cases.  Still work to do on finding the right
script, and setting globals/locals correctly when running an imported
function.

* Chane dfu.py to use Python 3 syntax to avoid dependency on Python 2.
* Update Makefile to call python instead of python2
* Fix #33

A big change.  Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object).  This scheme follows CPython.  Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.

Also change name prefix, from py_ to mp_ (mp for Micro Python).