Django-compat

- Fix error when installing package under python 3.4

- Django 1.9 compatibility with the following changes:
- `add_to_builtins` was removed for Django 1.9, still available for Django < 1.9
- `GenericForeignKey` was moved to `compat.models` for Django 1.9, can still be imported from `compat` for Django < 1.9
- `{% load url from compat %}` was added
- Added a systematic feature overview in `docs/compatibility.py`, which is also displayed in the README
- `get_model`

- Removed `get_queryset` <> `get_query_set` see, 29 because monkey patching does not fix the issue
- Added `add_to_builtins` support.
- Optimised Travis tests
- Universal wheel support
- Added tox configuration
- Added `commit` and `rollback` in atomic block
- dropped support for django 1.5

- added support for `Manager.get_query(_)set`
- added support for `(set_)autocommit`
- added tests for (set_)autocommit

- Added tests for format_html and resolve_url

- atomic
- commit_on_success, which is in alias for atomic
- format_html
- conditional_escape
- OrderedDict