Python callbacks

This pr adds two features to the python api. First PY-QUALIFIED-FROM for importing with a prefix. The other with-quot>py-cfunction so it becomes easy to make callbacks that you can pass to python functions. It's really fun to build these things on top of alien.
I'm not sure whether this makes sense, maybe you should ``&Py_Decref`` after adding to a container like this, but if you do, then shouldn't the ``hashtable`` below also use ``>py`` instead of ``(>py)``?