Add Python 3.10 support.

[hramezani]

• Add Python 3.10 support.
• Add pre-commit config file.
• Add Django main to test matrix.
• Add Python and Django supported versions badges.

[codecov[bot]]

Codecov Report

Merging #138 (35bd328) into master (55634e5) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #138   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          399       399           
  Branches        59        59           
=========================================
  Hits           399       399           

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[jezdez]

Thank you @hramezani!