Modularize flag parsing

[nakabonne]

No description provided.

[codecov-commenter]

Codecov Report

Merging #45 into master will increase coverage by 6.28%.
The diff coverage is 64.29%.

@@            Coverage Diff             @@
##           master      #45      +/-   ##
==========================================
+ Coverage   71.51%   77.78%   +6.28%     
==========================================
  Files           8        8              
  Lines         365      369       +4     
==========================================
+ Hits          261      287      +26     
+ Misses         86       63      -23     
- Partials       18       19       +1     

Impacted Files	Coverage Δ
main.go	79.21% <64.29%> (+23.54%)	⬆️

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