Add sections 12.5, 12.6 & 12.7 for GeoJSON, KML & DGGS

[nicholascar]

How to represent WKT & GML in RDF is indicated in the document but not GeoJSON, KML & DGGS which seem to have been missed.

GeoJSON has this class hierarchy (very flat):

GeoJsonObject
    Geometry
        Point
        LineString
        Polygon
        MultiPoint
        MultiLineString
        MultiPolygon
        GeometryCollection

So the same advice as per WKT & GML could be given for GeoJSON.

KML has

Object
    Feature
    Geometry
        Point
        LineString
        LinearRing
        Polygon
        MultiGeometry
        Model

DGGS???