Add difference / symmetricDifference

[brekk]

Functions for asserting the difference and commonality between two lists

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.03%. Comparing base (3187435) to head (c037022).
Report is 20 commits behind head on master.

❗ Current head c037022 differs from pull request most recent head 02ca01e. Consider uploading reports for the commit 02ca01e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
+ Coverage   74.00%   74.03%   +0.02%     
==========================================
  Files          81       81              
  Lines       11891    11877      -14     
==========================================
- Hits         8800     8793       -7     
+ Misses       3091     3084       -7     

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[brekk]

Pausing this until the weirdness is resolved

[aboeglin]

@brekk Should be fine now.

[brekk]

@aboeglin I nixed union for now, since I think writing it with Set is ultimately much more performant and not that hard to construct with composition. But otherwise I think these two difference functions are helpful as written.