One response to rule them all

This is a discussion piece.

Would be nice to leverage the filtering capabilities more for such things as rate limiting, caching, ability to support 304 responses ("Not modified"). However we need an ability to return a SS_HTTPResponse from preRequest filtering. 

Instead of overriding the entire return value, why not have only one persistent response object which we pass around so everyone can add stuff to it? And then the client code can set termination barriers to elect how early should the response terminate.