New pixel splitting implementation

[kif]

• [ ] should be able to deal with polygonal pixel with any size, (obviously 3, 4 and 6, but one could imagine edge splitting for better representativeness. The amount of work scales with the number of edges O(n), thus better than oversampling which is in O(n²)
• [ ] Probably implemented in Cython, but it would be a good use case for Rust + PyO3
• [ ] Define a Polygon class which constructor has just the number of edges (or vertices). One can reasonably assume a convex polygon, it simplifies some maths.
• [ ] Use setters to define vertices position
• [ ] Has a bounding-box, subtract the minimum integer position ...
• [ ] Has a isinside method to assess if a position is completely inside the polygon.