Expose triggerOnKeyPress and triggerOnKeyUp events for testing

I would like to set up a test harness for the CodeMirror text editor, and I didn't find a way to emulate keyboard events from javascript.
Nevertheless, I've found method `triggerOnKeyDown` that you exposed for testing purposes. If there were also methods `triggerOnKeyPress` and `triggerOnKeyUp`, then it would be possible to fully emulate key events for CodeMirror - here's [how I did it](https://gist.github.com/aslushnikov/8583301).

This pull request suggests exposing these methods from the codemirror. What would you say?