Add support for input event simulation.

We use 'input' event instead of 'keyup' in our project because we don't support old browsers and input event handles cases like copy paste. We wanted to write tests for our modules but currently there's no way to simulate "input" event so we're kind of stuck there. 
I've tested this code locally and it works fine. But I'm not totally sure about the side-effects of this change.
So I was hoping to get a guidance and some discussion in this pull-request.
I couldn't figure out what happens to people who don't use "node-event-html5" module. I'd guess they'd still be able to simulate the event but won't be able to listen to it.
I haven't setup a complete yeti test environment for yui so I couldn't run tests on this.