Replace setup.py in favor of pyproject.toml

[andruten]

Fixed the warning displayed during tests

$ python setup.py test
running test
WARNING: Testing via this command is deprecated and will be removed in a future version. Users looking for a generic test entry point independent of test runner are encouraged to use tox.
running egg_info
writing django_revproxy.egg-info/PKG-INFO
writing dependency_links to django_revproxy.egg-info/dependency_links.txt
writing requirements to django_revproxy.egg-info/requires.txt
writing top-level names to django_revproxy.egg-info/top_level.txt
reading manifest file 'django_revproxy.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
adding license file 'LICENSE'
writing manifest file 'django_revproxy.egg-info/SOURCES.txt'
running build_ext
Found 93 test(s).
Creating test database for alias 'default'...
System check identified no issues (0 silenced).
.............................................................................................
----------------------------------------------------------------------
Ran 93 tests in 2.619s

OK
Destroying test database for alias 'default'...

• Contributed pyproject.toml file
• Fixed django 3.x pipelines.
• Adapted tests

[codecov]

Codecov Report

Merging #173 (8e0ec9d) into master (d0099ea) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #173   +/-   ##
=======================================
  Coverage   98.53%   98.53%           
=======================================
  Files           7        7           
  Lines         410      410           
  Branches       70       70           
=======================================
  Hits          404      404           
  Misses          3        3           
  Partials        3        3           

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