[WIP] Locality Sensitive Hashing for approximate nearest neighbor search(GSoC)

The implementation in pairwise.py is optimised for matrix by matrix computation, whereas this version takes a vector as the first input (see @maheshakya's comment further on [1]). This function itself can be improved, but I missed that in my most recent pass. @maheshakya -- this function can be optimised by getting rid of the for loop