Refactor get_options calls
Fix sub-commands missing get_options invokations
Prompt user for missing change arguments

Several sub-commands accept one or more change IDs as arguments. If the
user doesn't pass any ID he'll be prompted with a menu of all
change-branches (and, perhaps, also change-tags, depending on the
command) for him to chose from.
Remove option --patchsets from 'prune'

There's no real use-case for this option, me thinks.
Implement sub-command 'list'

This new sub-command lists all existing change-branches and change-tags
in the local repository. It's sub-invoked at the end of the sub-commands
'update' and 'prune' too.
Change the function of 'checkout' sub-command

This is an incompatible change. The checkout sub-command now prompts
interactivelly, showing all existing change-branches and change-tags for
the user to chose which one should be checked out.
Implement the --tip option for the 'rebase' sub-command

The --tip option rebases just the commit at the tip of the change-branch
onto its upstream. It's useful to rebase a change created on top of some
cherry-picked commits after they have been merged on upstream.
Improve workflow documentation
Update bash completion
Improve documentation
Mention Barnum in the See Also documentation section
Re-fill POD and comments to 80 columns

This is a purely cosmetic change.