Add badges, update readme API options

[guybedford]

This adds the CI and coverage badges.

I've added the coverage call to the CI, but the token and setup may need some checking here first.

[guybedford]

Fixes #47.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@94ef030). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #78   +/-   ##
=========================================
  Coverage          ?   67.69%           
=========================================
  Files             ?        3           
  Lines             ?      260           
  Branches          ?        0           
=========================================
  Hits              ?      176           
  Misses            ?       84           
  Partials          ?        0

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