windows: Add modtime implementation
Merge pull request #575 from stinos/windows-modtime

Add modtime implementation for mingw
runtime0.h: Group binary ops by fives.

So one has some chance to convert numeric op code into symbol.
bytes: Implement comparison and other binary operations.

Should support everything supported by strings.
py: Fix base "detection" for int('0<hexdigit>', 16).
mingw: Fix compilation issues

- use lowercase windows.h
- fix for mingw32 using preprocessor-unfriendly definition of CLOCKS_PER_SEC
py: Rename byte_code to bytecode everywhere.

bytecode is the more widely used.  See issue #590.
stm: Reorder mpconfig.h header inclusion to get stm building.
stmhal: Fix setting of RTC: was BCD now BIN encoded.

Addresses issue #592.
py: Combine native emitters to 1 glue function; distinguish viper.

This patch simplifies the glue between native emitter and runtime,
and handles viper code like inline assember: return values are
converted to Python objects.

Fixes issue #531.
bare-arm: Change output file from flash.elf to firmware.elf.
py: Tidy up returning NULL which should be MP_OBJ_NOT_SUPPORTED.
objtype: Don't treat inheritance from "object" as from native type.

"object" type in MicroPython currently doesn't implement any methods, and
hopefully, we'll try to stay like that for as long as possible. Even if we
have to add something eventually, look up from there might be handled in
adhoc manner, as last resort (that's not compliant with Python3 MRO, but
we're already non-compliant). Hence: 1) no need to spend type trying to
lookup anything in object; 2) no need to allocate subobject when explicitly
inheriting from object; 3) and having multiple bases inheriting from object
is not a case of incompatible multiple inheritance.
objset: Give up and implement frozenset.

Tired of patching CPython stdlib for it.
py: Disable frozenset by default, enable on unix.

Takes 416 text bytes on x86.
modsys, unix: Add sys.exit(), should be implemented by a port.
stmhal: Implement draft version of sys.exit().
run-tests: Add support for skipping tests.

MicrpPython test should print single "SKIP" line for test to be skipped.
objset: Add frozenset tests, skippable if frozenset not available.
modsys: Enable sys.exit() per port after all.