Python3 Support

This pull request actually does 3 things, each in a separate commit in case you only want some of these things:

1. Adds python3 support.  This adds the [six](https://pythonhosted.org/six/) library as a dependency.
2. Adds a setup.py, partly because I want one (see #136) but also because:
3. Add tox, requires a setup.py but makes testing on multiple python versions much easier.

It also adds some more tests.  I ran through all the endpoints in my browser, and if the endpoint broke in Python3, I added a test for it.