Creates a new stop <Placemark/> element.

    Args:
      stop_folder: the KML folder the placemark will be added to.
      stop: the actual Stop to create a placemark for.
      style_id: optional argument indicating a style id to add to the placemark.

def _CreateStopPlacemark(self, stop_folder, stop, style_id):
    """Creates a new stop <Placemark/> element.

    Args:
      stop_folder: the KML folder the placemark will be added to.
      stop: the actual Stop to create a placemark for.
      style_id: optional argument indicating a style id to add to the placemark.
    """
    desc_items = []
    desc_items.append("Stop id: %s" % stop.stop_id)
    if stop.stop_desc:
      desc_items.append(stop.stop_desc)
    if stop.stop_url:
      desc_items.append('Stop info page: <a href="%s">%s</a>' % (
          stop.stop_url, stop.stop_url))
    description = '<br/>'.join(desc_items) or None
    placemark = self._CreatePlacemark(stop_folder, stop.stop_name,
                                        description=description,
                                        style_id=style_id)
    point = ET.SubElement(placemark, 'Point')
    coordinates = ET.SubElement(point, 'coordinates')
    coordinates.text = '%.6f,%.6f' % (stop.stop_lon, stop.stop_lat)