Docs: Add note to roadmap about creating alias for releasing gems
Feature: Change the width of subject line when using the log aliases

We're now expecting that the subject line is less than 72 characters so I'm
updating the log aliases to expect that.  This also means that the expectation
of the length of the tag/branch column needs to be adjusted accordingly.
Feature: Rename the 'prune' git alias to 'pb'

Git already has a command called 'prune' and this conflicted with it.  The
pneumonic for 'pb' is 'prune branches'.
Feature: Prune local branches where the tracking branch has been deleted

If a tracking branch for a local branch has been removed, git will show it in
the branch list as 'gone'.  Unfortunately there is no git command that I can
find which will remove those branches en masse.

This adds a command called `prune-gone-branches` which will do this.
Additionally, when the base `prune-branches` is called, it will also run this
command.