function swap(items, firstIndex, secondIndex){
    var temp = items[firstIndex];
    items[firstIndex] = items[secondIndex];
    items[secondIndex] = temp;
}
Swaps two values in an array.
@param {Array} items The array containing the items.
@param {int} firstIndex Index of first item to swap.
@param {int} secondIndex Index of second item to swap.
@return {void}