[MIXLIB-CLI-63] Add deprecated_option support

[marcparadise]

Description

This commit adds deprecated option support by exposing a
new ClassMethod, deprecated_option. It will generate a
corresponding deprecated option, and if that option is used it will
handle mapping of the old option to the new and issue a warning.

deprecated_option accepts a subset of the parameters that option accepts.

Most importantly, a deprecated option can't have a default value.
There's a practical reason for this and a philosophical one.

Practically, it makes it easy to track the situation where someone has
set use_separate_defaults to false. In that case, we currently
can't tell whether the user provided the flag, or it was set as a default.
This could have been addressed, but:

Philosophically it makes more sense to not have a default value on a
deprecated item. If it's deprecated, you want people to stop using it.
If it has a default, it's effectively forced in-use at all times.

See function docs for further accepted parameters.

To allow deprecated options without warnings, use parse_options as
parse_options(ARGV, show_deprecations: false). By default, warnings
will be shown.

This also moves some formatting code into its own class -
it was causing methods to get mixed in that client classes didn't
need; and I reached the point where I needed to access the formatting
functions across methods in both Mixlib::CLI and
Mixlib::CLI::ClassMethods. It made more sense to move them outside of
the mixed-in bits, since it wasn't a concern of the caller that would be
inheriting those methods.

Signed-off-by: Marc A. Paradise marc.paradise@gmail.com

Related Issue

Resolves #63

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• I have read the CONTRIBUTING document.
• I have run the pre-merge tests locally and they pass.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commits have been signed-off for the Developer Certificate of Origin.