[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
And finally please also add a note to state that on large datasets and large values of `n_hidden`, it is recommended to set `batch_size=1000` or similar to process a chunk of data at a time and use the internal sequential learner to avoid computing the non-linear feature expansion on the full training set at once.