Prefix program support

[henryiii]

This provides support for #13 .

[codecov]

Codecov Report

Merging #16 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #16   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           9      9           
  Lines        1036   1050   +14     
  Branches      217    220    +3     
=====================================
+ Hits         1036   1050   +14

Impacted Files	Coverage Δ
include/CLI/App.hpp	100% <100%> (ø)	⬆️
include/CLI/Validators.hpp	100% <0%> (ø)	⬆️

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