Django-slugify-processor

- Move doc URL from to git-pull.com
- Move travis -> gh actions
- Move pipenv -> poetry
- Move RTD -> self-hosted docs
- Relax package constraints
- Add package constraints for cases where python version / django effects things

- Get docs online
- Clean up API docs in code

- Add test_app, and tests for django-extensions and django-autoslug

- Try to tweak README / fix on PyPI

- README updates
- Support for overriding builtin slugify in templates
- Move template filter to _templatetags/slugify_processor.py_

- Initial commit

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