Make separate payload for the header.
Make release-fd payloads
capture_buffer -> peek_buffer to avoid a copy
remove release-buffer, we really need to release each fd in the buffer
separately.
provide_buffer -> send_buffer so that we can also use this to send the
release-fd messages.
in pinossrc, send back release-fd messages when the fd is no longer in
use.
Send a command stream over the socket.
Implement a new buffer object that holds the data and commands.
Make iterator and builders to parse and construct buffers.
Rework gstreamer elements to use new API for creating and parsing
buffers.
Add _release_buffer to notify a stream when we are done processing the
buffer. This will eventually go all the way to the server and will allow
us to do more complicated buffer management.
