Add support for server-side RTSP

[RouquinBlanc]

The parsing or the RTSP stream already supports receiving both requests and replies (and binary data).

It is now time to try adding support for implementing an RTSP Server.

Need to identify how far to go, but what is originally planned is:

• Multi-client support
• Flexible registration of streams and corresponding handlers
• Authentication (basic, digest)
• Basic example proxying a connection to another RTSP stream