Pass the client object around, it's easier to deal with than the sender
id.
Fix the ASYNC return check
Don't overwrite the fds of a pollitem, instead keep an index of their
position in the global fd array.
Add an async result code and an event to signal the completion.
Use async return values to signal completion of a method and potential
state change.
Add selected format to port update message.
Make it possible to parse into a custom copy of the command memory.
Remove state change events from the elements, we now just update the
state.
Implement async results in the proxy element
Add support for removing buffers in the client.
Fix up pinossink
Deal with async return in the links.
