Implement auto-termination

[abingham]

It probably makes sense for traad servers to kill themselves after a certain period of inactivity. This is similar to e.g. ycmd. This way clients don't need to be perfect about stopping servers.

This means that clients need to account for the possibility that a server will die. The emacs client does this already, and it doesn't seem too onerous.

[abingham]

There might be options for using a WSGI server like Rocket to handle this. It would be nice if the server had a native "auto shutdown" feature, but we might have to roll our own. For example, the WSGI server would handle connections in a separate thread. Another thread would have a timer that get reset on each connection. If the timeout was reached with no connections then the server would be killed and program terminated. How do we monitor connections on one thread from another? The WSGI server would need to provide some way of doing this, I guess.