Image2D interpolation

For the moment, interpolation in Pixpipe is only on sparse point set.

• 2D sparse dataset nearest neighbor | source - basic and not really an interpolation
• 2D sparse dataset triangulation | source - linear, not suited for non linear data
• 2D sparse dataset inverse distance weighting | source - a classic in GIS, though kind of flawed by local minimas
• 2D sparse dataset natural neighbors | source - close to the real function but slow to compute