[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 also add a link to the preprocessing chapter in the narrative doc. The appropriate ref is `preprocessing_scaler`. When the HTML is generated it should lead to: http://scikit-learn.org/dev/modules/preprocessing.html#standardization-or-mean-removal-and-variance-scaling