feat: dot notation

[phlptp]

Add the ability to use subcommand options using . notation
--sub.option or nested subcommands using dot notation.

[phlptp]

Still likely need to add more tests and some documentation updates

[phlptp]

from discussion on gitter

[codecov]

Codecov Report

Base: 99.29% // Head: 99.30% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (e7be7e8) compared to base (9a6c6f6).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #789   +/-   ##
=======================================
  Coverage   99.29%   99.30%           
=======================================
  Files          16       16           
  Lines        3974     4022   +48     
=======================================
+ Hits         3946     3994   +48     
  Misses         28       28           

Impacted Files	Coverage Δ
include/CLI/App.hpp	100.00% <ø> (ø)
include/CLI/impl/App_inl.hpp	99.23% <100.00%> (+0.02%)	⬆️
include/CLI/impl/Split_inl.hpp	98.70% <100.00%> (ø)

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[phlptp]

@henryiii I think this is ready now

[henryiii]

Is there a test for toml config with this? That was one of the reasons for it IIRC?

[phlptp]

The toml processing of dot notation worked before and is tested in a few locations, so this just adds to the command line parsing and doesn't change anything in the file parsing.