Discontinue support/testing for Python 3.3 with Django 1.8.
Closes#99
Focus Travis testing on currently-supported Django/Python combinations.
(But keep a few older ones in the matrix, too.)
* Set up tox for testing supported Django/Python combinations
* Also include tox env for checking and building docs
* Use tox-travis for Travis CI integration
* Add tests against Django master
* Document building docs and running tests with tox