Add support for Python 3.10

[hugovk]

Python 3.10 was released on 2021-10-04:

• https://discuss.python.org/t/python-3-10-0-is-now-available/10955

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The pylint errors are fixed in #175.

[codecov]

Codecov Report

Merging #176 (fc2be6b) into master (101d438) will not change coverage.
The diff coverage is n/a.

❗ Current head fc2be6b differs from pull request most recent head dd2836c. Consider uploading reports for the commit dd2836c to get more accurate results

@@           Coverage Diff           @@
##           master     #176   +/-   ##
=======================================
  Coverage   95.68%   95.68%           
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  Files           7        7           
  Lines         464      464           
  Branches       88       88           
=======================================
  Hits          444      444           
  Misses         10       10           
  Partials       10       10