Support parsing Placemark name

Over at PredPol, we use this library to figure out which district of a city a point is in. Because of the way the library works, we sometimes have to use multiple KML files to figure out which district a point falls in. 

If there was a way to figure out which Placemark each polygon belonged to, we could use a single KML file with multiple Placemarks instead, greatly simplifying things for us. I added a few simple lines to store the name of the Placemark each Polygon falls under to make this sort of thing possible.

Thanks for supporting this great library!