[MIXLIB-CLI-63] Add deprecated_option support

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:

Philosphically 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>

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