[MRG] 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
While testing the code, I found that `X` here is never sparse. The value of `X` is in fact either `H_batch` or `y_batch` which is incremented by `self.intercept_hidden_`  and therefore is forced into a dense matrix.

In other words, `if sp.issparse(X)` is always false.