Add Sphinx documentation and Travis-CI maintenance

As part of my GSOC'13 project, I updated Django Object Permissions documentation (it is now served [here](https://django-object-permissions.readthedocs.org/en/latest/)) and enabled travis-ci automated testing [service](https://travis-ci.org/pbanaszkiewicz/django_object_permissions) -- it's failing, but we can work on it.