[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
I would also add a note stating that some preprocessing is required to ensure that all input features vary approximately on the same scale, for instance by using a `Pipeline` with `StandardScaler` or `MinMaxScaler` as demonstrated in the `plot_elm_hyperparameters.py` example.