A self-hosted short URL plugin for Wordpress.
shortbread folder into
wp-content/plugins, and activate through the admin interface. Like you do.
Configure Shortbread under
Settings > Short URLs. Yes, it would arguably make more sense to put these settings on the Permalink page, but given that there's been a bug  open about that for four years now, it'll just have to wait.
As per WordPress's thoughts on the matter, this plugin is released under the GPL .