Revamp qstrs: they now include length and hash.

Can now have null bytes in strings.  Can define ROM qstrs per port using
qstrdefsport.h
diff --git a/py/objnone.c b/py/objnone.c
index 84d0ba1..ecc7c4b 100644
--- a/py/objnone.c
+++ b/py/objnone.c
@@ -4,6 +4,7 @@
 #include "nlr.h"
 #include "misc.h"
 #include "mpconfig.h"
+#include "qstr.h"
 #include "obj.h"
 
 typedef struct _mp_obj_none_t {