Supported Python & Django versions in the README are outdated

[austin-schick]

The README indicates

Supported Python versions: 2.7, 3.4+
Supported Django versions: 1.4-2.0+

and the "Known Bugs and Limitations" section makes quite a few references to Django 1.x

Since some backwards compatibility code was removed in #148, this is no longer the case.

[mikemanger]

I agree it would be good to make this clearer!

Just to add that setup.py still defines a min django version as 1.4 and doesn't specify Python 3.8 which is tested against and supported by Django 4.2.

Not as important but I think these files also need updating to make it clearer:

• tox.ini
• workflow could test full range of python versions

The project could do with a pyupgrade tidy up, a few of the files still have python 2 -*- coding: utf-8 -*- header comments. This might be outside the scope of this issue though.