Finds the k nearest neighbours for every point in a given dataset using Jose Luis' 'nanoflann' library. There is support for exact searches, fixed radius searches with 'kd' trees and two distances, the 'Euclidean' and 'Manhattan'. For more information see <https://github.com/jlblancoc/nanoflann>. Also, the 'nanoflann' library is exported and ready to be used via the linking to mechanism.
copied from cf-post-staging / r-rnanoflann