Pulled in and modified work done by mux/iabdalkader on cc3k driver, from
iabdalkader-cc3k-update branch.  That branch was terribly messy and had
too many conflicts to merge neatly.

Images are currently served from micropython.org/static.  I don't know
if there is a better way to handle images.

The JSON specs are relatively flexible and allow us to use one function
to print strings, be they ascii, bytes or utf-8 encoded.

Addresses issue #864.

It seems most sensible to use size_t for measuring "number of bytes" in
malloc and vstr functions (since that's what size_t is for).  We don't
use mp_uint_t because malloc and vstr are not Micro Python specific.

Also do the same for teensy timer code.

Add pulse_width_percent to teensy.

Fix stmhal and teensy print routines to report actual prescaler an period.
Fix teensy build to use soft-float
Add USE_ARDUINO_TOOLCHAIN option to teensy build

mp_parse_node_free now frees the memory associated with non-interned
strings.  And the parser calls mp_parse_node_free when discarding a
non-used node (such as a doc string).

Also, the compiler now frees the parse tree explicitly just before it
exits (as opposed to relying on the caller to do this).

Addresses issue #708 as best we can.

windows: Enable input(), sys.maxsize(), ujson module, emergency exceptio...

Fix unix/Makefile to build on OSX

Add more specific comments describing what is going on.

Stack is full descending and must be 8-byte aligned.  It must start off
pointing to just above the last byte of RAM.

Previously, stack started pointed to last byte of RAM (eg 0x2001ffff)
and so was not 8-byte aligned.  This caused a bug in combination with
alloca.

This patch also updates some debug printing code.

Addresses issue #872 (among many other undiscovered issues).

Force OSX to compile with clang even if gcc is available
Change LDFLAGS syntax to be compatible with clang
Fix questionable syntax on line 90
Remove extraneous tab character

This allows to set the pulse width (for PWM mode) as a ratio relative to
the period of the timer.  Eg, 0.5 is a 50% duty cycle.  You can set the
ratio in the channel init, or using channel.pulse_width_ratio; the
latter can also read the pulse width as a ratio.

Also add start of ujson module with dumps implemented.  Enabled in unix
and stmhal ports.  Test passes on both.

Heap RAM was being allocated to print dicts and do some other types of
iterating.  Now these iterations use 1 word of state on the stack.

Deleting elements from a dict was not allowing the value to be reclaimed
by the GC.  This is now fixed.

By measuring SD card addresses in blocks and not bytes, one can get away
with using 32-bit numbers.

This patch also uses proper atomic lock/unlock around SD card
read/write, adds SD.info() function, and gives error code for failed
read/writes.