Switch docs to mkdocs

[brews]

• [ ] closes #xxxx
• [ ] tests added / passed
• [x] docs reflect changes
• [x] entry in CHANGELOG.md

Switch docs from pdoc to mkdocs. Why not?

[codecov[bot]]

Codecov Report

Merging #235 (f519bfe) into main (b5a93fe) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #235   +/-   ##
=======================================
  Coverage   89.34%   89.34%           
=======================================
  Files           8        8           
  Lines        1352     1352           
=======================================
  Hits         1208     1208           
  Misses        144      144           

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