Display \r and \t escape codes in string repr
Improve REPL detecting when input needs to continue.

Full CPython compatibility with this requires actually parsing the
input so far collected, and if it fails parsing due to lack of tokens,
then continue collecting input.  It's not worth doing it this way.  Not
having compatibility at this level does not hurt the goals of Micro
Python.
Merge pull request #451 from lurch/repr-fixes

Display \r and \t escape codes in string repr
py: Improve GC locking/unlocking, and make it part of the API.
py: Continue line if last character is backslash.
windows: Use most of the source files from unix/ port.

To keep it maintainable, windows port now uses as much as possible from
unix port.  Maybe could even use mpconfigport.h.
Add a check for NULL nlr_top in nlr_jump.

If no nlr_buf has been pushed, and an nlr_jump is called, then control
is transferred to nlr_jump_fail (which should bail out with a fatal
error).
unix: Oops, remove nlr_jump test in main.
stmhal: in EXTI interrupt handler wrap uPy calls in gc_lock and nlr_buf.
py: Improve compiler syntax errors; catch more errors.
py: Raise exception for unimplemented byte codes.
bytearray: Support bytearray(int) constructor.

To create bytearray of given length.
bytes: Support buffer protocol.
unix modffi: Support any object implementing buffer protocol as a native arg.
py: implement UNPACK_EX byte code (for: a, *b, c = d)
py: Improve inline assembler; add a few more opcodes.
Merge branch 'master' of github.com:micropython/micropython
py: Make bytearray a proper type.
py: Finish implementation of all del opcodes.

At this point, all opcodes are now implemented!

Some del opcodes have been combined with store opcodes, with the value
to store being MP_OBJ_NULL.
Merge branch 'master' of github.com:micropython/micropython