A mechanism to ensure that the parser will only parse requests or only parse responses

[bvanderveen]

As described by @sergey-litvinov on #10:

• update IHttpParserDelegate just to have common methods between request and response (Headers, Body, etc).
• create two interfaces IHttpRequestParserDelegate and IHttpResponseParserDelegate that will inherit IHttpParserDelegate with Request\Response specific methods.
• two constructors for HttpParser.
  • one receives IHttpRequestParserDelegate.
  • one receives IHttpResponseParserDelegate.
• two member variables
  • one IHttpParserDelegate variable
  • a flag as to whether the delegate is a IHttpRequestParserDelegate or a IHttpResponseParserDelegate
• in the request/response-specific embedded actions, check the flag on and throw and exception if the value is unexpected