Set the default configuration file output as TOML

[phlptp]

Address the TOML issue in #384.

This PR changes the default config file output to be TOML compliant. It should not change input since input files can be toml or the previous INI format, so this PR is not a breaking change for input configuration and output configuration should be readable on input, but if the configuration is used elsewhere it could be considered a breaking change.

• add a bunch of tests for toml output and input,
• update the readme
• update the book chapter on config
• tweak the reader to handle both toml and ini for comments and vector input.

[codecov]

Codecov Report

Merging #435 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #435   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          12     12           
  Lines        3582   3583    +1     
=====================================
+ Hits         3582   3583    +1

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

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