We can't allocate the shared meta in shared mem because then clients can
damage it for other clients. Place it instead right after the buffer
metadata array. Filter out the shared metadata for a client, we send it
as part of the client_buffer structure.
Remove pointer metadata, it's not so useful.
Document the layout of the allocated buffers and the shared memory.
Work on metadata to define control parameters
ringbuffer: remove size and mask from the ringbuffer, we have that
elsewhere in the user of the ringbuffer.
Remove the buffer data offset and size fields and replace with a
ringbuffer. We then have a ringbuffer in all buffer data, which
simplifies things.
We can now remove the ringbuffer metadata.
