help_heading for subcommands

[tailhook]

It would be nice to have help_heading equivalent for the subcommands. Currently there is App::help_heading but it does something different (default help_heading for next arguments).

This is needed for the commands having a lot of of subcommands, to show you one example, here is a snippet from virsh (command-line tool for libvirt):

 Domain Management (help keyword 'domain')
    attach-device                  attach device from an XML file
    attach-disk                    attach disk device
    attach-interface               attach network interface
    [.. snip ..]
 Domain Monitoring (help keyword 'monitor')
    domblkerror                    Show errors on block devices
    domblkinfo                     domain block device size information
    domblklist                     list all domain blocks
    domblkstat                     get device block stats for a domain
    domcontrol                     domain control interface state
    domif-getlink                  get link state of a virtual interface
    [.. snip ..]
 Host and Hypervisor (help keyword 'host')
    allocpages                     Manipulate pages pool size
    capabilities                   capabilities
    cpu-baseline                   compute baseline CPU
    cpu-compare                    compare host CPU with a CPU described by an XML file
    cpu-models                     CPU models
    [.. snip ..]

[epage]

Looks like this is a duplicate of #1553 . If this is by mistake, feel free to comment, letting us know!