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.
Not totally sure. Python makes a big difference whether containers steal references or not. And its really hard to test (afaik) whether a reference leak has occured or not.