Rework the wire protocol

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.

src/gst/gstpinossrc.h

@@ -62,6 +62,8 @@ struct _GstPinosSrc {
   PinosContext *ctx;
   PinosStream *stream;
   GstAllocator *fd_allocator;
+
+  GstBuffer *current;
 };
 
 struct _GstPinosSrcClass {