NF: SurfaceQueryEngine, intended to find surface Dataset features that are within a particular (Euclidean or dijkstra) distance from a center node
ENH+RF: make fa_key an argument (rather than use "node_indices"), plus some minor refactorings as suggested by @yarikoptic
ENH: let __str__ and __repr__ show the new fa_node_key value
Merge pull request #173 from nno/_tent/surfqe

NF: SurfaceQueryEngine; identify feature indices in neighborhood for surface dataset