Revamp qstrs: they now include length and hash.

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

py/qstr.h

@@ -0,0 +1,35 @@
+// See qstrraw.h for a list of qstr's that are available as constants.
+// Reference them as MP_QSTR_xxxx.
+//
+// Note: it would be possible to define MP_QSTR_xxx as qstr_from_str_static("xxx")
+// for qstrs that are referenced this way, but you don't want to have them in ROM.
+
+enum {
+    MP_QSTR_NULL = 0, // indicates invalid/no qstr
+    MP_QSTR_ = 1, // the empty qstr
+#define Q(id, str) MP_QSTR_##id,
+// TODO having 'build/py.' here is a bit of a hack, should take config variable from Makefile
+#include "build/py.qstrdefs.generated.h"
+#undef Q
+    MP_QSTR_number_of,
+} category_t;
+
+typedef machine_uint_t qstr;
+
+#define QSTR_FROM_STR_STATIC(s) (qstr_from_strn((s), strlen(s)))
+
+void qstr_init(void);
+
+qstr qstr_from_str(const char *str);
+qstr qstr_from_strn(const char *str, uint len);
+//qstr qstr_from_str_static(const char *str);
+qstr qstr_from_strn_take(char *str, uint alloc_len, uint len);
+//qstr qstr_from_strn_copy(const char *str, int len);
+
+byte* qstr_build_start(uint len, byte **q_ptr);
+qstr qstr_build_end(byte *q_ptr);
+
+machine_uint_t qstr_hash(qstr q);
+const char* qstr_str(qstr q);
+uint qstr_len(qstr q);
+const byte* qstr_data(qstr q, uint *len);