Feature request: Move job logic out of Backend\Base class

[adamwight]

I like the idea of keeping before & after hooks on every action in the Base class, but what do you think about decoupling the job tracking (last_job_id and open_items) into a new class? Or even isolating all job queue logic in a new component? Plain old queue stuff is a useful service to provide in a library, on its own!

Also, I don't understand how the before and after hooks would be overridden. Maybe there should be an example in the demo/ dir? I ask because I'm thinking about removing or refactoring these functions, if they aren't being used.

[adamwight]

On second thought, maybe last_job_id is still useful for general queue purposes, but could be rolled into Message::$id, and all the get/pop functions will return a Message wrapper around the data?