Add PlainTextPrinter

[kimikage]

This also adds tests for HTMLPrinter.

Closes #6

[codecov]

Codecov Report

Merging #12 (d4ac2b5) into main (d969688) will increase coverage by 45.05%.
The diff coverage is 94.11%.

@@             Coverage Diff             @@
##             main      #12       +/-   ##
===========================================
+ Coverage   50.49%   95.54%   +45.05%     
===========================================
  Files           3        4        +1     
  Lines         202      247       +45     
===========================================
+ Hits          102      236      +134     
+ Misses        100       11       -89     

Impacted Files	Coverage Δ
src/html.jl	89.47% <ø> (+47.36%)	⬆️
src/plain.jl	80.00% <80.00%> (ø)
src/ANSIColoredPrinters.jl	95.30% <97.56%> (+73.37%)	⬆️

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