Add control properties to audiotestsrc for frequency and volume
and add a test program.
Add size parameter to set_io for additional checks and to make it
easy to know how much control data we can write.
Make it possible to configure multiple io areas on a port by giving
an id to set_io.
Add some types to enumerate the supported ids
Make an area to exchange buffers and one to specify pull ranges.
The idea is to make more area types for controlable properties.
Implement enumeration of IO areas in volume.
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
Add an argument to pass the result param to the caller instead of
having the caller have to pick it up from the builder.
Improve docs for node, clock and monitor
Pass spa_pod everywhere instead of spa_pod_object.
Pass result argument to spa_pod_filter to make things a little
nicer.
