Niche-vlaanderen

* Add validation module, allowing the user to compare the result of a niche model with an actual vegetation map.
* Improved speed of zonal statistics.
* Detailed plot splitting up unsuitable types to soil unsuitable/mxw unsuitable+ other conditions.
* Add support for recent Python versions (3.10 and 3.11).
* Important notice:
* Python 2 is no longer supported. Python 3.7 is the minimum version required. >=3.9 recommended.

* Work with asymmetrical cells (204)
* Add check for new versions of niche_vlaanderen (180)
* Fix a number of warnings for newer versions of Affine and Numpy (207)
* New install instructions for Windows (260)
* Important notice:
* This is the last version supporting Python 2. Switching to Python 3 is highly recommended.