EventListener.js - new Audio() throws exception in IE 10 !!! Fixed with check in try-catch
GameSettings.js - gong.mp3 is replaced with gong.wav that supports Firefox and other browsers
Polyfill.js is added - polyfill requestAnimationFrame for old browsers
styles.css - changed cursor to 'crosshair'
main.js - calls Polyfill.js and shim requstAnimationFrame if necessary