Add rust implementation

[jianshu93]

A beautiful Rust implementation. I have run benchmarks for various dataset with very good performance and recall. More metric distance are supported including hamming, Hellinger distance, Jensen-Shannon distance between probability distributions (f32 and f64). There is A Trait to enable the user to implement its own distances. It takes as data slices of types T satisfying T:Serialize+Clone+Send+Sync.