Tests improvements

[browniebroke]

• Run tests on Python 3.5 and 3.6
• Make a requirements file
• Switch to codecov

[coveralls]

Coverage remained the same at 84.835% when pulling 3715f91 on tests into 896bc10 on master.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@896bc10). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #13   +/-   ##
=========================================
  Coverage          ?   85.89%           
=========================================
  Files             ?       33           
  Lines             ?      716           
  Branches          ?        0           
=========================================
  Hits              ?      615           
  Misses            ?      101           
  Partials          ?        0

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[coveralls]

Coverage remained the same at 84.835% when pulling 9cd1fab on tests into 896bc10 on master.