Polygon: merge from trunk. New functionality: Voronoi diagram, segment concept, segment utils.
Polygon: merging recent trunk fixes: removing all static data from the Voronoi headers; fixing lazy sss predicate logic.
Polygon: Merging trunk and release branches.
Added tests and refactored data/traits/concept classes for point/interval/segment.
Removed point_3d point/interval/segment.
Simplified transform (3D->2D).
Fixed bugs: #6366, #7678.
Polygon: fixing duplicate bookmark in the documentation.
Polygon: Sync public interface of point/segment/interval data with documentation.
[Polygon] Merging from trunk for the upcoming release: 1) Updated Voronoi documentation. 2) Fixed #8026, #8197, #8257.