Remove synexpand and friends

[gilch]

^*#, ^#–^^^^#

Closes #227.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b4fed74) 98.89% compared to head (d7c8219) 98.89%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #251   +/-   ##
=======================================
  Coverage   98.89%   98.89%           
=======================================
  Files           6        6           
  Lines         726      726           
  Branches      112      112           
=======================================
  Hits          718      718           
  Misses          4        4           
  Partials        4        4           

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[gilch]

Maybe I can replace some of this with simpler pieces, but that's for later, if ever.