[WIP] Initial Python 3.3 support

There is a problem with `PyString_FromStringAndSize(char *s, Py_ssize_t len)` in Python 3 (see issue #1).
```
-    object PyString_FromStringAndSize(char *s, Py_ssize_t len)
+    object PyBytes_FromStringAndSize(char *s, Py_ssize_t len)
```
I've amended test cases to be Python 3 friendly too. Please have a look.