We save some code bytes by using builtin string functions.

Also improve precision of calculating PWM percent in integer mode.
Also update teensy with edge case fix.

Added pyb.elapsed_millis and pyb.elapsed_micros

teensy: Enable 8-byte stack alignment for IRQ Handlers.

Fix error: unknown type name 'size_t'

Fix timer overflow code.

tested using:
stmhal: https://github.com/dhylands/upy-examples/blob/master/elapsed.py
teensy: https://github.com/dhylands/upy-examples/blob/master/teensy/elapsed.py

Teensy doesn't need to worry about overflows since all of
its timers are only 16-bit.

For PWM, the pulse width needs to be able to vary from 0..period+1
(pulse-width == period+1 corresponds to 100% PWM)

I couldn't test the 0xffffffff cases since we can't currently get a
period that big in python. With a prescaler of 0, that corresponds
to a freq of 0.039 (i.e. cycle every 25.56 seconds), and we can't
set that using freq or period.

I also tested both stmhal and teensy with floats disabled, which
required a few other code changes to compile.

It seems that newer versions of clang don't like the .bss directive, so
we don't use it for OSX.

Addressing issues #865 and #875.

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).