Add an install script

Had some free time today (but not enough to tackle any serious features) so I wrote an installer / upstart job.

This means that:
* It'll always be installed in the same place
* It'll always log to the same place
* You can control it with standard commands `service txircd (start|stop|status)`
* It starts on boot

without preventing the existing way of doing things.
I've written up some instructions on both methods of running things.

Possible future work: Automatically set up a seperate linux user for txircd to run as (this is quite easy with upstart).