Drop support for Python 2, Django 1.11 and 2.2. Add support for Python 3.7+ and Django 3.0+

[SupImDos]

Description

Closes #77

We use django-anon in our project, which we are in the process of upgrading through django versions 3 -> 4 -> 5.

This package still appears to be compatible with at least Python 3.7+ and Django 3.0+, so I've updated the tests, CI and documentation to confirm and reflect this. Given that Python 2, Django 1 and Django 2 are no longer supported, I've dropped them from the tests, CI and documentation.

See the following for CI testing results: https://github.com/BrightpathProgress/django-anon/actions/runs/7707166404

Its also probably worth updating isort / flake8 / black, as well as removing some compatibility related code for Python 2.7, Django 1 and Django 2, but I've omitted that to reduce noise / unnecessary changes.

Changes

• Drops support / testing for Python 2, Django 1.11 and Django 2.2
• Adds support / testing for Python 3.7+ and Django 3.0+

Todos

• Tests
• Documentation
• Changelog