chore(ci): add tests and coverage via Github Actions

[troggy]

• Using Github Actions instead of Travis.
• Uploads coverage to codecov.io (wasn't uploaded with Travis)

Reason for Github Actions:

• native, no need to open external site
• once adopted, allow extra automations (e.g. greeting contributors etc)

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@48453d2). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #170   +/-   ##
=========================================
  Coverage          ?   82.89%           
=========================================
  Files             ?       13           
  Lines             ?     1093           
  Branches          ?        0           
=========================================
  Hits              ?      906           
  Misses            ?      187           
  Partials          ?        0

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Continue to review full report at Codecov.

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