Python 3.0 porting docs started in the wiki

Some docs to cover how to port code to Python 3.0 has been started in the wiki. The goal is to get the docs into a good enough shape such that they can go into the official documentation.

If you end up contributing to the docs (and please do!), see Georg's announcement email where he mentions things you can do to help make it easier when these docs are converted over for the official docs.