start of queues

still needs to be done:

* adding the queues to the sql
* figure out how to specify what queues to listen on. environment variable?
* figure out how to add the queues to the job.
  - maybe via a class attribute in the job class?
* others probably
Merge branch 'master' into queue
Support custom retry intervals for certain job classes (closes #10).
Merge branch 'queue' of https://github.com/joevandyk/que
Finish support for named queues. Documentation to come.