Add Support for Circular Paths (in KML files)

[wp99cp]

On maps.geo.admin.ch, if you draw a circular path, the path gets saved differently:

<Polygon><outerBoundaryIs><LinearRing>
	<coordinates>...</coordinates>
</LinearRing></outerBoundaryIs></Polygon>

On the other hand, a linear path is saved as follows:

<Placemark><LineString>
	<coordinates>...</coordinates>
</LineString></Placemark>

Currently, our KML parser do not support circular paths.

An example of such a path can be found here: https://github.com/ckolin/marschzeittabelle/blob/main/samples/map_loop.kml