Hybrid pycnophylactic-dasymetric interpolation

[asinghvi17]

https://doi.org/10.1080/01431161.2010.496805 proposes an interesting method for pycnophylactic interpolation based on a boolean mask, or potentially even something more complex.

Once we have pycnophylactic interpolation implemented, this wouldn't be too hard to build on top of that. We'd need to think of a good name for it though - maybe MaskedPycnophylactic or WeightedPycnophylactic?