function position(e) {
      var offset = sigma.utils.getOffset(_target);

      return {
        x: e.pageX - offset.left,
        y: e.pageY - offset.top
      };
    }
The user inputs default captor. It deals with mouse events, keyboards
events and touch events.

@param  {DOMElement}   target   The DOM element where the listeners will be
                                bound.
@param  {camera}       camera   The camera related to the target.
@param  {configurable} settings The settings function.
@return {sigma.captor}          The fresh new captor instance.