Django 1.6 compatibility and more

- Django 1.6 compatibility
- ``compat.py`` to deal from Django 1.4 to 1.6
- ``tests`` directory
- multiple tox environments to run test suite from Python 2.6 - Django 1.4 to Python 3.3 - Django 1.6

The coverage from the initial project is very slow, so let me know if you want more stuffs.