Session

I think that either we make different modules for different kinds of Session datastore methods, 

or somehow specify the method to be used via the constructor and another variable provided to yap -- yap('Session','PHP'), yap('Session','APC') which would pass that along to the Session constructor which would determine how to handle data.

or in one module with multiple classes yap('SessionPHP'), yap('SessionMemCached'), yap('SessionAPC') and the manifest specifying src files would choose the correct class to instantiate.

An option to handle sessions via database would be good as well.  

A lot of ways to handle this, and it would be good to choose the least complicated way, so that all module services will have a common interface.