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

actually:

```python
n_candidates_values = np.linspace(10, 500, 5).astype(np.int)
```

and:

```python
n_estimators_values = np.linspace(1, 30, 5).astype(np.int)
```

seem to be enough. In particular the accuracy reaches a plateau for `n_estimators ~= 15` so going to `n_estimators=30` is more than enough to highlight this.