Feature: Add git-versions subcommand

It displays all version tags on the repo.  It can handle various version
styles such as:

* 0.10.0
* 0.10.0
* 0.10
* 0.10beta1
* 0.10-beta-1
* 0.10.0.rc.1

Any of these styles can have an optional `v` in front of them like so:

`v0.10.0.beta1`

Additionally, any of the above styles can have an optional `release` or
`releases` in front as a way to organize into folders in a git GUI.

* release/0.10.0
* releases/v0.10.0beta1

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Branch:        feature/add-plugin-for-releasing-gems
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>
Feature: Non-existent remote branches no longer show errors

Previously when deleting a remote branch that didn't exist (via rmb) it
would show an error.  We don't care.