More docs, regression + efficient weight update
More docs, regression + efficient weight update

This commit has the following updates:

(1) NeuralNet2 now has the capability of performing
linear and non-linear regression.

(2) User now has the option of modifying the output
layer activation function. To perform regression, specify
the output layer to be 'linear'.

(3) Allow the user to specify a network without hidden
layers.  This performs simple linear regression if the
output layer activation function is linear and logistic
regression if the output layer activation function is
a sigmoid.

(4) Performed a more efficient weight update with
matrix multiplication rather than the sum/bsxfun approach.

(5) More documentation through `help NeuralNet2` showing
how to perform binary classification, non-linear regression
and multi-class classification.  Documentation also shows
classification accuracy when showing classification examples.

StackOverflowMATLABchat/NeuralNetPlayground