Convert God init script into upstart script

As Unicorn and MailCatcher are already started via upstart, I think it makes sense to use it for God too.

([Upstart](http://upstart.ubuntu.com/) is the standard init daemon under Ubuntu.)

Usage is super easy:

```
root@practicingruby:/home/vagrant# status god
god start/running
root@practicingruby:/home/vagrant# stop god
god stop/waiting
root@practicingruby:/home/vagrant# start god
god start/running
root@practicingruby:/home/vagrant# god status
practicing_ruby:
  practicing_ruby_delayed_job: init
root@practicingruby:/home/vagrant# god status
practicing_ruby:
  practicing_ruby_delayed_job: up
```