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 agree - changing the input parameters is never a good practice (can't believe I missed that).

Should it be a public attribute `self.gamma_` or a private `self._gamma`? because I am not sure if `self.gamma_` is necessary for the user who would've read the documentation to see how `gamma=None` is inferred.