@davecheney it is kinda a leaky part of how the martini service mapping works. Since it is common for middleware to override responsewriter, mapping to `martini.ResponseWriter` would require that overwriters map both types, http.ReponseWriter and martini.ResponseWriter. It is kind of kludgy, but I think It will avoid more confusion to just use http.ResponseWriter.

Maybe in the near future we can allow for injection via implementers instead of concrete types and direct interfaces only. There is still a bit to think through on this subject