Restart using `exec` and file descriptors (hot restart)

This implements a hot restart with Sanford. With this, there are
no dropped connections and the server will essentially, pick up
where it left off after restarting. This is to provide no downtime
when a server needs to be restarted to pull in changes.
Merge pull request #54 from redding/jcr-add-hot-restart

Restart using `exec` and file descriptors (hot restart)