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

Should just be:
```python
accuracies_c[i] = ratio
```
or
```python
accuracies_c[i] = np.sum(neighbors_approx == neighbors_exact) / n_queries
```
(you can avoid he `float` around `n_queries` by including `from __future__ import division` above)