Just simple, if you use this plugins, rel=nofollow and target=_blank will be insert automatically, for all the external links of your website posts or pages.
Nothing for now
The basic structure of this plugin was cloned from the WordPress-Plugin-Boilerplate project.
This plugin supports the GitHub Updater plugin, so if you install that, this plugin becomes automatically updateable direct from GitHub. Any submission to WP.org repo will make this redundant.