Implementation of stopImmediatePropagation

I implemented [stopImmediatePropagation](https://nodejs.org/api/events.html#eventstopimmediatepropagation) with a really simple change. In the emit prototype loop that executes the listeners I check the ReflectApply return for the string 'stopImmediatePropagation'. To stop a event propagation the event handler then returns 'stopImmediatePropagation'.

Will this break something? Is there interest in adding this?