The `fromParts` factories take geometry instances instead of coords

The MultiLineString case was correct here.  The MultiPoint and MultiPolygon cases should be using the constructor instead of the `fromParts` factories.
KML MultiGeometry may contain other MultiGeometry

As demonstrated in the tests, a MultiGeometry may contain other MultiGeometry nodes.  We can support this with heterogenous GeometryCollection instances - though these are not currently rendered.
Merge pull request #829 from tschaub/kml

Parse MultiGeometry in KML