prettySize: convert bytes to a more readable string.
function prettySize(bytes) {
        var s = ['bytes', 'kb', 'MB', 'GB', 'TB', 'PB'];
        var e = Math.floor(Math.log(bytes)/Math.log(1024));
        return (bytes/Math.pow(1024, Math.floor(e))).toFixed(2)+" "+s[e];
    }