Added support for GeoJSON MultiPolygon with holes

To determine if a polygon has multiple parts with or without holes I walk each ring and each time a clockwise ring is parsed it is added as a new polygon part. Each time a counter-clockwise ring appears it is added to the previously parsed clockwise ring and forms only one polygon together with holes.

If there is more than one clockwise ring in a feature the geometry type is set to "MultiPolygon".

I used this this file as reference (page nr. 8): http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf