function getEventLocation(element,event){
  // Relies on the getElementPosition function.
  var pos = getElementPosition(element);
  
  return {
    x: (event.pageX - pos.x),
      y: (event.pageY - pos.y)
  };
}
return the location of the click (or another mouse event) relative to the given element (to increase accuracy).
@param {DOM Object} element A dom element (button,canvas,input etc)
@param {DOM Event} event An event generate by an event listener.