Add multi-operations using a defer flag when saving an item.
Declare PHP 5.3 dependency.
Add constants to help clarify whether to save immediately or not.
Adds setExpiration() method.
Switch to a separate saveDeferred() method.
Clarify that implementors must always commit deferred data eventually.
Remove the vestigial delete() method from cache items.
Remove now-duplicate documentation that is part of the spec itself.
Merge pull request #5 from Crell/multi-set

Multi set support