Generate documentation with mdoc

[fthomas]

This allows us to use variables from the build in the docs.

[codecov]

Codecov Report

Merging #2315 (509a898) into master (63704fa) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2315      +/-   ##
==========================================
+ Coverage   79.71%   79.73%   +0.01%     
==========================================
  Files         137      137              
  Lines        2376     2378       +2     
  Branches       59       65       +6     
==========================================
+ Hits         1894     1896       +2     
  Misses        482      482              

Impacted Files	Coverage Δ
.../core/edit/scalafix/ScalafixMigrationsLoader.scala	100.00% <100.00%> (ø)
...ore/update/artifact/ArtifactMigrationsLoader.scala	100.00% <100.00%> (ø)

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