Radius search

[VarIr]

Currently, approximate radius neighbor search is only available via falconn.
The new version of NGT v1.7.10 seems to introduce a radius search function.
Would be nice to have an additional radius search provider (which, moreover, isn't LSH).

[VarIr]

With the removal of falconn from scikit-hubness, there is no radius search left. While nice to have, radius search is not of particularly high interest to hubness research. Therefore, removed from the TODO list for v0.30.