Python 3.3 compatibility

As well as making it compatible, I've added classifiers. Classifiers are important to signify Python 3 compatibility, and are used by
 + PyPI's [Python 3 Package List](https://pypi.python.org/pypi?:action=browse&c=533&show=all), and
 + [caniusepython3.com](http://caniusepython3.com)