Reset the builder when the filter failed.
Make the plugins create their params in a temporary buffer, we
don't want to do in-place filtering because that is not always
possible. Because the filter now resets on error, we can remove
the reset from the plugins.
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.
