First working version!

Obviously it doesn't work *as well* as I want it to yet, but it will
call your worker with jobs on the registered queue. It currently
doesn't:

 - Parse the json for the job. Obviously this is important.
 - Update statistics that resque uses.
 - Handle more than one job per second.
 - Make any use of Rust's nice concurrency capabilities.
 - Have a particularly good API.
 - Have enough tests.

But a good start!