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
Also, 
```
In [62]: %timeit X.copy().ravel()[::1001] += 4.2
100 loops, best of 3: 3.14 ms per loop
```
which avoids the 2 x len(X) index vectors generated by `np.diag_indices` at the cost of legibility (I think this is the trick used in the ridge code)