Add pyproject.toml

[markgras]

Addresses issue #80

[codecov]

Codecov Report

Merging #81 (c71222a) into master (dbc4867) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #81   +/-   ##
=======================================
  Coverage   99.45%   99.45%           
=======================================
  Files           4        4           
  Lines        1102     1102           
=======================================
  Hits         1096     1096           
  Misses          6        6           

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[markgras]

Note that the minimum setuptools version requirement still supports Python 2.7. Once Python 2 support is dropped, that version can be bumped.