Revamp qstrs: they now include length and hash.

Can now have null bytes in strings.  Can define ROM qstrs per port using
qstrdefsport.h
Merge branch 'master' of github.com:micropython/micropython

Conflicts:
	py/objstr.c
	py/py.mk
	py/stream.c
	unix/main.c
	unix/socket.c