Rewrite socket handling in Python

The former 'bjoernmodule.c' file (the one you imported with
'import bjoern') has been reimplemented in Python.

This Python code contains high-level socket handling.

The interface to the C server code is now no more than the
'bjoern.server_run(sock, wsgi_app)' function which is passed
a PYTHON socket and the WSGI application.

This allows to run bjoern on arbitrary socket(-like) objects, easing
integration with 3rd party frameworks.

The old high-level API ('bjoern.run', 'bjoern.listen') remains intact.

This refactoring has been motivation by issue #73.
Merge branch 'rewrite-socket-initialization'