Support of Http Response parsing

Hey,

I've added logic for parsing Http Responses too. I've updated Ragel rules, and also added new method to `IHttpParserDelegate` - `void OnResponseCode(HttpParser parser, int statusCode, string statusReason);` as it needs to be tracked in by parser. Also i've added a couple of unit tests to test new rules, and verified that old one still works.

Also i updated readme file to include update delegate signature

Could you please review it when you have time for that, merge, and push new NuGet package? Thanks!