Implement fastpair (#142)

* initial fastpair implementation
* FastPair initial implementation
* implement fastpair
* Add random test
* Add bench for fastpair
* Refactor with constructor for FastPair
* Add serialization for PairwiseDistance
* Add fp_bench feature for fastpair bench

src/algorithm/neighbour/mod.rs

@@ -41,6 +41,10 @@ use serde::{Deserialize, Serialize};
 pub(crate) mod bbd_tree;
 /// tree data structure for fast nearest neighbor search
 pub mod cover_tree;
+/// dissimilarities for vector-vector distance. Linkage algorithms used in fastpair
+pub mod distances;
+/// fastpair closest neighbour algorithm
+pub mod fastpair;
 /// very simple algorithm that sequentially checks each element of the list until a match is found or the whole list has been searched.
 pub mod linear_search;