Add GitHub workflow

[ericpre]

• Move CI from travis to github actions,
• add coverage,
• add release workflow,
• update badges,
• ready for review.

Close #18 and #31.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@79f6ce2). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master     #32   +/-   ##
========================================
  Coverage          ?   8.06%           
========================================
  Files             ?      13           
  Lines             ?     409           
  Branches          ?       0           
========================================
  Hits              ?      33           
  Misses            ?     376           
  Partials          ?       0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 79f6ce2...352f66f. Read the comment docs.