Suggestion: support synchronous events/emit

[zhaoyao91]

I am impressed by the api design of this library, but a big case does need support of synchrounous events: to proxy react input onChange event.

If this event is emitted asynchronously, the composition input like Chinese, Japanese will all fail down.

[vitaly-t]

@zhaoyao91 If you need synchronous events, maybe sub-events will be of some use ;)

It lets you specify optional EmitSchedule, which is synchronous by default, when emitting the event:

event.emit(data, {schedule: EmitSchedule.next});