GitHub actions

[iamdefinitelyahuman]

What I did

• Use Github Actions for CI instead of Travis - closes Move CI from Travis to Github Actions #56
• Use Codecov for coverage instead of Coveralls (related - coverallsapp/github-action:#30)
• Update tox.ini and setup.cfg

How to verify it

Verify that tests are now running on actions and coverage report is displayed on codecov.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@f2ba8d0). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #59   +/-   ##
=========================================
  Coverage          ?   76.93%           
=========================================
  Files             ?        8           
  Lines             ?      581           
  Branches          ?      132           
=========================================
  Hits              ?      447           
  Misses            ?      105           
  Partials          ?       29           

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