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/.
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...).