Modified file include accordingly

 - Revert default value of span. - Removed api test for 3D because it could lead to issues when ctests run in parallel (tests would open the same files at the same time which would cause high latency. - Fixed values of Rae 3D case wrt to previous fix

Plus fixed a bug that would set span to 0

API only works for 2D cases

Fixed API, dart interface and prevented segfault if the number of sections is not imposed correctly.

Contains 2D and 3D developements as well as the api.