A lot of improvements

1) Optimization_method parameter for selecting any scipy optimizer
2) SGD is also supported
3) Improved minibatch creation using scikit's gen_even_slices (much
faster)
4) Support of loss functions
squashed last 35 commits
Fixed tanh derivative and added a test case for it
Fixed doc issues
A preliminary version of MLP with more than one hidden neuron
Improved the documentation and multi-layer perceptron speed
improved documentation
Improved the documentation
Added a fix for python3 expit problem
Addressed latest comments
Typo fixed
Fixed lbfgs iterations count
fixed typo
removed unnecessary computations in the unpacking method
Changed the verbs into indicative form
fixed doc
Added convergence warning
Example of mlp with/without pretraining
Cleaner Pre-training algorithm
Pre-training using make_pipeline