Add dummy bytes() constructor.

Currently, MicroPython strings are mix between CPython byte and unicode
strings. So, conversion is null so far. This dummy implementation is
intended for compatibility with CPython (so, same code can run on both).
diff --git a/py/mpqstrraw.h b/py/mpqstrraw.h
index 10b1fc0..9bc01c5 100644
--- a/py/mpqstrraw.h
+++ b/py/mpqstrraw.h
@@ -40,6 +40,7 @@
 Q(array)
 Q(bool)
 Q(bytearray)
+Q(bytes)
 Q(callable)
 Q(chr)
 Q(complex)