キーボードのキーが押されました。
Use Event.character to find out what has been typed. Use Event.keyCode to handle arrow, home/end or other function keys, or to find
out which physical key has been pressed.
This event is sent repeatedly depending on the end user's keyboard repeat settings.
Note that key presses can come as separate events, one with valid Event.keyCode, and another with valid Event.character.
In case of keyboard layouts with dead keys, multiple Event.keyCode events can generate a single Event.character event.