Support auto-start option in queues.

With this option users can decide whether the queue will automatically start processing items or wait for the start method to be called.

The main use case for this is synchronizing multiple independent queues. When qA finishes processing I want to start qB, then when it's done I want to start qC. Even though qB and qC are not processing items it's easier if they accept defers anyway.

If there's anything I can do to improve the code and/or docs to help approve this pull request let me know.

I also would like to install this module using bower. I can do the bower infrastructure in another pull request if that's something you'd consider valuable.