Change references to SigmoidalLayer to HiddenLayer

The SigmoidalLayer and TahnLayer classes seem to have been merged into
the HiddenLayer with has an activation function attribute. Several
places in the tutorial still refer to the SigmoidalLayer, so I updated
them to HiddenLayer and took care to specify the T.nnet.sigmoid
activation function where appropriate.
Merge pull request #30 from zacstewart/master

Change references to SigmoidalLayer to HiddenLayer