function insert(item, array, compareFunction) {
  var location = locationOf(item, array, compareFunction);
  array.splice(location, 0, item);
  return location;
}
Fast quicksort insert for sorted array -- based on:
 http://stackoverflow.com/questions/1344500/efficient-way-to-insert-a-number-into-a-sorted-array-of-numbers
@param {any} item
@param {array} array
@param {function} [compareFunction]
@returns {number} location (in array)
@memberof Core