Shuffle string
/**
* Shuffle string like crazy
*
* @param {int} length desired
* @return {string} the shuffled string
*/
String.prototype.shuffle = function(size) {
var arr = this.split('');
for(var j, x, i = arr.length; i; j = parseInt(Math.random() * i), x = arr[--i], arr[i] = arr[j], arr[j] = x){};
arr = arr.join('');
return size ? arr.substr(0, Math.min(size, arr.length-1)) : arr;
};