Add documentation for Geometry3d

Warning, you must merge #287 before this pr.
This pr contains the documentation of:
* `ST_TriangleAspect`
* `ST_TriangleContouring`
* `ST_TriangleDirection`
* `ST_TriangleSlope`
* `ST_Force3D`

See #289
@ebocher I think the problem is [here](https://github.com/irstv/H2GIS/blob/a8e61ea7f1953d1bad194af926a568f7bc9aac96/h2spatial-ext/src/main/java/org/h2gis/h2spatialext/function/spatial/topography/ST_TriangleAspect.java#L66). Why do you rotate by `Math/PI / 2`?