event: split PyPP

Also, don't ref events in Loop. Log error when destroying loop with
registered events.
event: C++ify modules. pybus: get rid of __pending
C++ify PyArg and use it. Rename Long to Int. Add String (incomplete).
event: Add module clear. Use NullMethods for Object::py__*
C++ify threads and floats.

test/introspect.py still causes kernel panic.