Ability to control ordering/grouping of commands in help text

[vito]

My CLI has a few commands that I'd like to call out for easier discoverability, e.g. login should be listed first. Currently commands are ordered alphabetically, which is a sane default especially when the AddCommand flow is used (since the order is not well-defined with func init()).

Some way to influence the ordering, or even better, having a way to group commands together (similar to option groups) would be nice. For example, in large CLIs you'll often have a set of commands relevant to a particular object type.

[vito]

Here's an example that would be helped by this kind of thing:

https://github.com/concourse/fly/blob/20980dc/commands/fly.go

Note that there's semantic grouping in the struct itself (which I'd happily group further if the group struct tags applied), which gets lost in the help text.

[jessevdk]

I think allowing to place commands in groups would work pretty well. This requires some reorganization, but should be doable.