* This initial implementation is a bit hackish, but it uses a normal middleware API
    so it's future-proof when we improve the internals.

Renamed ActionController::Renderer to ActionController::Responder and ActionController::MimeResponds::Responder to ActionController::MimeResponds::Collector.

This commit breaks all exception catching plugins like ExceptionNotifier. These plugins should be rewritten as middleware instead overriding Controller#rescue_action_in_public.

Build query string and POST params parser on top of Rack::Request. Also switch our multipart parser to use Racks. Moved XML, JSON, and YAML parsers into ActionController::ParamsParser middleware [#1661 state:resolved]