PyBindGen documentation

I have been prodded by the NS-3 guys, namely Mathieu Lacage, to provide more documentation for PyBindgen. Additionally he provided some nice and short examples of C/C++ code to wrap. I then wrote the PyBindGen code that wraps the C/C++ examples, and added everything to the repository.

I looked into it and decided to use epydoc to generate API docs. Additionally I wrote a small introductory section, just to get started (else it's easy to get lost with all the classes). So here it is, the first draft of PyBindGen API documentation. Enjoy.