Removed explicit bias term, tanh activation fun

Changes for the neural network: bias matrix nn.b included in the weight
matrix nn.W; normalization of inputs; usage of the tanh activation
function with optimal parameters (see LeCun's "Efficient BackProp");
updated tests
moved bias add to nntrain, fixed examples
fixed numerical gradient checking. fixed sparsity.
updated readme
Merge pull request #20 from rasmusbergpalm/master-experimental

Optimal tanh activation functions, bias included in weights, numerically test most permutations of parameters