[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
Please add an inline comment that explains that `regularized_HT_H` has a very low probability of being a singular matrix because of:
- the random projection of the first layer
- the regularization introduced when `C` is not extremely large

Therefore it is safe to use `linalg.solve` instead of the `linalg.lstsq` solver that tend to be slower especially when the number of samples in the data batch is small.