add EventTarget event handlers to node window

the use case is to be able to run [mercury component](https://github.com/ahdinosaur/grid-ui) [tests](https://github.com/ahdinosaur/grid-ui/blob/master/test/index.js) in node that involve [window event handlers](https://github.com/ahdinosaur/grid-ui/blob/065bcb5b688b1cf5f099a91b7f649c0e37a43390/lib/edgeEvent.js#L74-L79).

i'm not sure if this commit is necessarily the best way to do this, seems hacky. i was thinking maybe we can define a more proper window in min-document, but then again maybe each of these DOM interfaces ([EventTarget](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget), [document](https://developer.mozilla.org/en-US/docs/Web/API/document), [Element](https://developer.mozilla.org/en-US/docs/Web/API/Element), [window](https://developer.mozilla.org/en-US/docs/Web/API/window), ...) should be separate modules, or i don't know.

cheers!
this `extend` does a copy, this might not be what we want.