GSoC 2014: Standard Extreme Learning Machines

Finished implementing the standard extreme learning machines (ELMs). I am getting the following results with 550 hidden neurons against the digits datasets,

Training accuracy using the logistic activation function: 0.999444
Training accuracy using the tanh activation function: 1.000000

Fortunately, this algorithm is much easier to implement and debug than multi-layer perceptron :).
I will push a test file soon.

@ogrisel , @larsmans
You might always to keep

```
            if self.algorithm == 'recursion_lsqr':
                # K_{0} = H_{0}^T H_{0}
                self._H_sub = safe_sparse_dot(H_batch.T, H_batch)
```

Since you might want to do
```
elm = ELMRegressor().fit(X, y)`
elm.partial_fit(X_new_batch, y_new_batch)
```

What do you think?