Demonstrates populating a PointTrack layer with gx:Track elements from KML.
                If a KML document contains <gx:Track> 
                elements and the extractTracks property is set true on the 
                parser, features will be created that represent track points.
                These track points can easily be visualized as track lines with
                a PointTrack layer, preserving the KML's original
                styles.
            
View the kml-pointtrack.js source to see how this is done.