A new OGRGeometryH based Geometry class

[sgillies]

In https://github.com/Toblerity/fiona-rfc/blob/master/rfc/0001-fiona-2-0-changes.md#details the downsides of a GeoJSON-based geometry object are enumerated. An extension class based on OGRGeometryH could make it easy to handle every kind of geometry that OGR can.