Apply black to the codebase

[mdickinson]

One-time application of of black to the codebase, to clean up some of the more egregious style issues. This isn't something we expect to repeat on a regular basis.

For ease of recreation: the black version used was:

mirzakhani:envisage mdickinson$ black --version
black, version 19.10b0

And the exact command issued was:

mirzakhani:envisage mdickinson$ black --line-length 79 --target-version py35 .

No other changes were made to the codebase in this PR.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@174a7f3). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #267   +/-   ##
=========================================
  Coverage          ?   53.06%           
=========================================
  Files             ?      135           
  Lines             ?     4425           
  Branches          ?      518           
=========================================
  Hits              ?     2348           
  Misses            ?     2033           
  Partials          ?       44

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[corranwebster]

I got bored about halfway through the changes. Looks fine modulo the disagreements I have with Black's style choices.