* Fixed the describe bug - Content-Length refers to the body of the
message being replied, i.e. in this case: the sdp
* Moved some of the more basic RTSP fields to the response class
* Added 'content' to the rtsp response
* Handling of Content-Length is done in the response
Refactored out the header parsing of the incoming request
Merge branch 'respond_with_sdp_to_describe'