Improve handling of SIGINT interrupts

[odow]

Closes #620

I tried a bunch of different approaches. This seemed like the most robust.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.52%. Comparing base (28325ac) to head (751dd20).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #621   +/-   ##
=======================================
  Coverage   93.51%   93.52%           
=======================================
  Files           6        6           
  Lines        2714     2718    +4     
=======================================
+ Hits         2538     2542    +4     
  Misses        176      176           

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