(minor) Make attributes of NeighbourWrapper @properties
It would be nice if
self.specie, self.spec_encoded_row, self.cartesian_row, self.cartesian_col were properties. I was tinkering with
NeighbourWrapper and wondering why
None. It took me a a while to figure out I needed to run
compute_distances to populate them. I see there's already ValueError raised here, but it's only raised when
rdf is called. If these attributes were promoted to properties one could simple raise this exception everytime
self.species is called.