Colorful help

[dkaszews]

Python's argparse library can produce colorful help messages as of 3.14, which would be a nice thing to have in CLI11 as well.

I think it greatly improves readability, visually breaking up large blocks of text and highlighting positional, short and long options.

That would be a nice addition.

[Zhou-London]

I am looking into this.
Seems a very feasible improvement. Adding a new subclass of Formatter, say, ColorFormatter, injecting some ANSI codes in overrides, should be able to make it.