Django-sorting-bootstrap

- Change in format for docs to Markdown
- Use of Black and flake8
- Drop of Python 2
- Drop of Django 1.x
- Use of Poetry
- Removing useless tests

- Fixed import error with Django 1.8+ (issue 6), thanks to gabrielfast.
- Created basic Travis-CI integration (tests are needed).
- Improved documentation.

- Changed raise statement to work with Python 3
- Adds support for Django < 1.5
- Better modularization. Thanks to caioariede.
- Fix on to use request.path instead of ./ when possible. Thanks to caioariede.
- Fixed rst2html.py (docutils 0.8 - for compliance with PyPI) warnings in README.rst.
- Reoganized README.rst for better understanding.

- Bug-fix in autosort for ChangeList usage

- Bug-fix in sort_headers current_sort_field comparison
- No use of Python reserved word sorted (now is is_sorted)
- Optimization in has_visible_name - it was taken off for better working