Adding Python 2.6 support, some cleanup

I added in lib2to3 from Python 2.7.3 and modified some tests, the library now runs on Python 2.6. This doesn't increase the size of the lib too much, so I think it's an okay solution.

I also edited the tox.ini file to only check 2.6 and 2.7.

Most of the cleanup was in the setup.py file, simplifying it and adding some classifiers.