Port to python3.x & Django 4.0+

[elrandira]

Small contributions, I wanted to see what was rfdoc about.

From Omenia's fork, who started porting to Python3, I continued porting to python3.

I, simply, stackoverflow-ed all the issues I found while trying to run on Django 4.0 (never seen so many functions being deprecated/removed in a package) and managed to have a local running version.

If this is of any use to anyone, you are welcome.

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Tested on Windows only with the following steps:

1. execute python setup.py install
2. execute python -m rfdoc.rfdocsettings_defaults /your/path/here to create a rfdocsettings.py
3. edit rfdocsettings.py to your needs
4. add /your/path/here to PYTHONPATH or use parameter --pythonpath=/your/path/here in the commands below:
5. execute python -m rfdoc.manage migrate --run-syncdb
6. execute python -m rfdoc.manage runserver