thread safe, update nanoflann

[j042]

Overview

• fixes thread-unsafe radius_search and radii_search
• adds std::vector<T> classes with py::bind_vector. this is a return type for radius searches.
• format
• add query_ball_point, similar to scipy's API
• fixes #17
• update nanoflann
• add leaf_size param for init
• add nthread param for init -> used for concurrent tree build
• adds unique_data_and_inverse()