Also make stdout_print_strn static (ultimately this function needs to be
merged with stdout_tx_strn).

Still some method names to iron out, and funtionality to add, but this
will do for the first, basic version.

This renames:
MICROPY_PY_FROZENSET -> MICROPY_PY_BUILTINS_FROZENSET
MICROPY_PY_PROPERTY -> MICROPY_PY_BUILTINS_PROPERTY
MICROPY_PY_SLICE -> MICROPY_PY_BUILTINS_SLICE
MICROPY_ENABLE_FLOAT -> MICROPY_PY_BUILTINS_FLOAT

See issue #35 for discussion.

Blanket wide to all .c and .h files.  Some files originating from ST are
difficult to deal with (license wise) so it was left out of those.

Also merged modpyb.h, modos.h, modstm.h and modtime.h in stmhal/.

It's really a UART because there is no external clock line (and hence no
synchronous ability, at least in the implementation of this module).
USART should be reserved for a module that has "S"ynchronous capabilities.

Also, UART is shorter and easier to type :)

With this fix, all tests in tests/basics pass on pyboard.

This adds support for almost everything (the comma isn't currently
supported).

The "unspecified" type with floats also doesn't behave exactly like
python.

Tested under unix with float and double
Spot tested on stmhal

New USB HAL is quite a bit improved over previous one.  Now has better
callbacks and flow control.

REPL over USB CDC now works as before, except for soft-reset (since USB
driver uses malloc...).

MICROPY_ENABLE_FLOAT is automatically set in mpconfig.h if MICROPY_FLOAT_IMPL
is set to a non-zero value.

In particular, unix outputs to stderr, to allow to run testsuite against
micropython built with debug output (by redirecting stderr to /dev/null).

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

See pyb_usart_global_debug variable.

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

You can now append a zipfile (containining uncomressed python sources)
to the micropython.hex file.

Use MEMZIP_DIR=directory when you call make, or set that in your
environment to include a different tree of source files.

Added sample /boot.py, /src/main.py, /test.py and /src/test.py files.

Added run command so that you can execute scripts from REPL (until import is implemented).

Added build directory to .gitignore

* Add Micro Python bindings to usart.c
* Export USART python object to namespace pyb