Extend coord_within for use with any polygon?

[maelle]

I.e. wrapping something like sf::st_within (or whatever the wkt tool is if that's better) in order to allow to filter observations within a given polygon.

One might need to do that when getting data from APIs that only accept a bounding box or circle as filter.

[sckott]

good idea. we do already use sp in this pkg, so we can leverage that to do this i think