WIP: Key simulation

This implements a simple form of triggering commands and insertions by simulating keys. Like:

```js
var keys = require('ace/lib/keys');
keys.simulateKey(editor, 'Shift-Right');
keys.simulateKey(editor, 'Command-Shift-d');
keys.simulateKey(editor, 'Control-a');
/*...*/
```

todo:

- [ ] support series of keys (like `keys.simulateKey(editor, 'Right Right Command-Down')`)
- [ ] base `keys.send` / old vim sendKeys code onto simulateKey