Re: [RFC/PATCH] parse-options: introduce parse_subcommands

>   $ git notes foo
>   error: Unknown subcommand: foo
>   usage: git notes [--ref <notes_ref>] [list [<object>]]
>      or: git notes [--ref <notes_ref>] add [-f] [-m <msg> | -F <file> | (-c | -C) <object>] [<object>]
>      or: git notes [--ref <notes_ref>] copy [-f] <from-object> <to-object>

> is replaced by a more helpful:
>
>   $ git notes foo
>   error: unknown subcommand: foo
>   usage: git notes [<options>] [<subcommand>] [<options>] [<object>..]
>
>   available subcommands:
>       list                  list notes for given object
>       add                   add notes for given object
>       copy                  copy notes for first object onto second object
>       append                append notes to existing object
>       edit                  edit notes for given object
>       show                  show notes for given object
>       merge                 merge given notes ref into current notes ref
>       remove                remove notes for given objects
>       prune                 remove all notes for non-existing/unreachable objects
>       get-ref               print the current notes ref