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
Given you docstring, you want to compute the activation. It doesn't look like a get operation (like in the dict).
Maybe you want to say something like `_activate_hidden_layer` (22 characters)/ `_apply_hidden_layer` (19 characters) instead of `_get_hidden_activations `(23 characters).