stream method
listen to an event on this ProEventEmitter as a stream. An ProEvent
will be emitted whenever the event by this name is emitted.
Use the special event
name of 'all' to subscribe to all events.
Implementation
Stream<ProEvent> stream(String event) {
return eventStream.stream.where((e) => e.name == event); //.map<bool>((event) => true);
}