audit usages of `evaluate`

[ericphanson]

I tried to ensure that #654 fixed the last issue here by checking each usage of evaluate in src (outside of the problem depot). I added comments to a few places, and updated the dev docs.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.89%. Comparing base (379f7e7) to head (5b0d66f). Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #655   +/-   ##
=======================================
  Coverage   97.89%   97.89%           
=======================================
  Files          88       88           
  Lines        5125     5125           
=======================================
  Hits         5017     5017           
  Misses        108      108           

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