Add ConcaveHullOfPolygons class

[dr-jts]

Adds a class ConcaveHullOfPolygons to compute concave hulls using a set of polygons as a constraint. The computed hull respects the polygon boundaries (i.e. the hull is guaranteed to contain the polygons). (In contrast the existing ConcaveHull class operates only on the vertices of the input, and the result hull may not contain all the area of polygons provided as input.)

The concaveness of the hull is controlled by a target criterion which may be one of;

• the Maximum Edge Length of the triangulation of the "fill" area between the polygons
• the Maximum Edge Length Ratio - a scale-free factor of the difference between the longest and shortest edge in the fill area triangulation
  These criterion are the same ones provided for the current ConcaveHull class.

Additional parameters are:

• whether or not the hull is "tight" to the outside boundary of the input polygons;
• whether holes are allowed in the hull.

The fill area can be computed as well.