[FUTURE] More control over raster extent in `interpolate_raster` function

[SimonMolinsky]

At this stage algorithm produces numpy array which is a box and data is interpolated outside the study area. The idea is wrap interpolate_raster function into more complex package with:

• greater control over area extent,
• possibility to use vector masks,
• return GeoJSON output,
• and maybe something else...?

This idea will be exploited in the future and it is a proposition of further development.