Previously, the content had to be a null-terminated byte
sequence because the sending function used `strlen()` to
determine its length. However, `rtsp_do_auth_setup()` needs
to send a non-textual byte sequence, and it only worked so
far because it did not happen to have any zero bytes in it.
Add a "content_length" parameter and change the type of
"content" to facilitate sending arbitrary byte sequences.
Handle control source io. We don't yet implement retransmission,
though.
Handle latency by exposing the server latency on the stream ports.
Use the Format param event to connect/announce and teardown.
Use the stream state to record/flush.
Fix some leaks.
Remove the state from rtsp-client, we don't need it.
Strip whitespace from header values.
