Now of the form MICROPY_PY_*.  See issue #35.

Done in generalized manner, allowing any stream class to be specified as
working with bytes.

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/.

Specifically, nlr.h does.