Remove signals.
Rename callbacks -> events, use listeners to listen for events.
Callbacks are still used in spa for things you can listen to only
once.
Fix docs
Add some more versions to interfaces
Make types for the various proxy object + inline methods that does type
checking and create proxys etc.
Set owner client of client-nodes in the properties
Pass type to bind to in create-node
Don't place global id in the info structs
Improve registration of marshal functions
Pass more types around as ids
Add hooks that contain protocol specific interfaces that can be used
to extend the protocol. This makes it possible to add new interfaces
to the protocol and implement the protocol specific data transport.
Move these protocol specific extension to the extensions directory.
