Keyboard navigation in choices

Hi,

I have added proper keyboard navigation in choices for multi select.
- It is possible to navigate to the choices by pressing the left arrow or backspace on the keyboard when the carret of the textbox is at the beginning without deleting the text.
- Navigation between choices is possible with arrow keys
- Selected choice is deleted with delete or backspace on the keyboard.
- An event is fired when a choice is selected ("choice-selected" and "choice-unselected")
- Choices can be selected with the mouse.

See http://jsfiddle.net/YHT2W/ for demo.