Allow complex input geometries

[jannikmi]

allow input of complex geometries: input coords, and edges (index reference to two coords)
This is a more general data format for all kinds of geometries. Polygons are special case and should be converted to the more general data format then.

special case: empty boundary polygon
In some use cases the environment might only consist of obstacles (=holes).
-> support not providing a boundary polygon.

[jannikmi]

Note: with just independent line segments as input, the concept of "inside" and "outside" does not exist.
all edge vertices would be "extremities" -> inefficient
-> allow passing edge indices of polygons (consequent segments creating a loop)

Question: can one vertex be reused in more than 2 edges? yes, multiple overlapping "polygons". how to decide "inside" / "outside" angles?!