Remove context and extensions, make client API also use the core.
Make a new pw_remote object that keeps connections with remote
instances.
Remove introspection API, it's just as easy to connect to the registry
and get updates like that.
Expand the protocol a little to make it useful for making listeners
and connections.
Move protocol specific connection to the module. Make some new
convenience methods.
Make a factory to create nodes from spa objects
Add an example of a local pipeline displaying a v4l2 source.
Rework the node and port API so that other implementations can be used
than the spa_node. The plan is to morph this into the stream and
context API.
Rework the graph API a little so that init + add is separated.
