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

This example can be greatly sped up by only computing 5 points on a log scale:

```
n_candidates_values = np.logspace(1, 3, 5).astype(np.int)
```

Examples are run when building the documentation, so it's very important to try to make them run as fast as possible while keeping them realistic enough to highlight interesting properties of the estimators.