Add ignore underscore

[phlptp]

If merged this pull request will add an option for ignore_underscore which allows options to be triggered equivalently such as option_one and optionone

This also applies to sets and subcommands.

The code style is a mimic of what is done for ignore_case so hopefully that should be easy to follow.

There are two failing test cases but they are same issue as #170 so can be removed.

[codecov]

Codecov Report

Merging #185 into master will decrease coverage by 0.05%.
The diff coverage is 98.71%.

@@            Coverage Diff             @@
##           master     #185      +/-   ##
==========================================
- Coverage     100%   99.94%   -0.06%     
==========================================
  Files          12       12              
  Lines        1744     1818      +74     
==========================================
+ Hits         1744     1817      +73     
- Misses          0        1       +1

Impacted Files	Coverage Δ
include/CLI/App.hpp	100% <100%> (ø)	⬆️
include/CLI/StringTools.hpp	100% <100%> (ø)	⬆️
include/CLI/Option.hpp	99.65% <96.29%> (-0.35%)	⬇️

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[codecov]

Codecov Report

Merging #185 into master will decrease coverage by 0.05%.
The diff coverage is 98.71%.

@@            Coverage Diff             @@
##           master     #185      +/-   ##
==========================================
- Coverage     100%   99.94%   -0.06%     
==========================================
  Files          12       12              
  Lines        1744     1818      +74     
==========================================
+ Hits         1744     1817      +73     
- Misses          0        1       +1

Impacted Files	Coverage Δ
include/CLI/App.hpp	100% <100%> (ø)	⬆️
include/CLI/StringTools.hpp	100% <100%> (ø)	⬆️
include/CLI/Option.hpp	99.65% <96.29%> (-0.35%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c3d8d4a...bebcb9a. Read the comment docs.

[henryiii]

I like it, the one codecov issue is a bit odd and can be fixed later. I'll go ahead and merge, then add changelog notes later.

[henryiii]

Thanks!