[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
Could you also make it possible to pass user specified `sample_weight` in the `fit` and `partial_fit` method. Also please add a smoke test to check that `AdaboostClassifier(base_estimator=ELMClassifier())` works without crashing when calling fit on a toy dataset.