add Lm (Letter, modifier) to small letter char

[ichiban]

#212 (comment)

[codecov]

Codecov Report

Merging #240 (7ffc3d8) into main (8bbdd2c) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #240   +/-   ##
=======================================
  Coverage   97.53%   97.53%           
=======================================
  Files          21       21           
  Lines        6764     6764           
=======================================
  Hits         6597     6597           
  Misses        136      136           
  Partials       31       31           

Impacted Files	Coverage Δ
engine/lexer.go	100.00% <100.00%> (ø)

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