Cleaner errors

[henryiii]

This improves the error messages using the simple formatter. Errors are restructured, and some error code names have changed.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@b45917e). Click here to learn what that means.
The diff coverage is 100%.

@@           Coverage Diff           @@
##             master    #53   +/-   ##
=======================================
  Coverage          ?   100%           
=======================================
  Files             ?      9           
  Lines             ?   1298           
  Branches          ?    257           
=======================================
  Hits              ?   1298           
  Misses            ?      0           
  Partials          ?      0

Impacted Files	Coverage Δ
include/CLI/App.hpp	100% <100%> (ø)
include/CLI/Error.hpp	100% <100%> (ø)
include/CLI/Ini.hpp	100% <100%> (ø)
include/CLI/Option.hpp	100% <100%> (ø)

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