ENH: Add license checks

[ericdill]

This adds checks to avoid mirroring agpl or unlicensed conda packages internally. cc @parente @mariusvniekerk

[codecov-io]

Current coverage is 92.85% (diff: 100%)

Merging #7 into master will increase coverage by 1.94%

@@             master         #7   diff @@
==========================================
  Files             2          2          
  Lines            77         98    +21   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits             70         91    +21   
  Misses            7          7          
  Partials          0          0          

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[mariusvniekerk]

LGTM