Fully functioning feed forward and back-propagation NN.

This release contains following features:

1. Uses CMake build system, the programs are written completely in C++11.
2. The executable takes options from command line (uses gnu command line options); see '--help' for all options.
3. Feed forward and back propagation methods implemented (test programs to emulate boolean AND, OR, XOR attached).
4. Two factory methods which can create single layer and double layer feed feed-forward Neural network.
5. Can print the state of neural network in graphviz format.