function elementsFromPoint (x, y) {
  return (document.elementsFromPoint) ? document.elementsFromPoint(x, y) : elementsFromPointPolyfill(x, y)
}
Returns an array of HTML elements located under the point specified by x, y.
If the native elementsFromPoint function does not exist, a polyfill will be used.

@param  {number} x : X position
@param  {number} y : Y position
@return {array} : Array of the elements under the point (x, y)