Upstart support

I've added support for Upstart scripts (thanks to [sidekiq](https://github.com/mperham/sidekiq/tree/master/examples/upstart) for the base! :)).

It still have lots of room for improvement but it's quite simple and, from my experience, it works better than the init.d alternative.

It doesn't support multiple users (I couldn't make upstart take setuid from a variable) and I don't know if baking in the extra logic actually makes sense, since you can always clone the schema for as many users as you have and achieve the same results.

Btw, the init.d version could also be simplified, particularly by removing the add/remove config capabilities and following the same logic I followed with upstart.

Thoughts?