Scrap the individual adapter system, it's no longer necessary.
Minor comment cleanup.
Rename Que::Adapter to Que::Pool, it's more descriptive.
Add Que.in_transaction? and Que.checkout as shortcuts.
Use Forwardable to clean up the base module a bit.
Minor clean up in ResultQueue.
Minor Pool cleanup.
Refactoring - move some logic out of Que::Pool.