Proposal: Allow grouping of options for help

[DougC]

Really liking the library. I recently started using it for a project and it's the easiest and most flexible command line parser I've come across.

On feature I'd like to see is a way to group a set of flags together and provide help text for that group. I imagine something like:

(opt1, opt2).mapN(GroupedOptions.apply).groupedAs("Options for debugging")

Then the help generator could group these options together with the extra text.

[bkirwi]

I like this! There's a few details that would need to be worked out -- desired behaviour if group names are reused or the same option is added to different groups -- but I think we should be able to do something sensible and valuable here.

I'm unlikely to find time to work on this in the next couple weeks, but would definitely welcome contributions with this shape.