ENH: Only classes belonging to API are now contained in 4neuro.h. All those classes were enclosed in 'lib4neuro' namespace.

ENH: Removed both linking and include dependencies from examples => lib4neuro can be used just by linking it and including its header without any external dependencies needed.

Updated the structure and functionality of NeuralNEtwork class to account for the changes in connections and neurons.
Updated the logic in DESolver to account for the changes in NeuralNetwork