added a constant file and more neuron classes

.idea/usage.statistics.xml

CMakeLists.txt

src/CMakeLists.txt

src/Neuron/NeuronBinary.cpp

src/Neuron/NeuronBinary.h

src/Neuron/NeuronLinear.cpp

src/Neuron/NeuronLinear.h

src/Neuron/NeuronLogistic.cpp

src/Neuron/NeuronLogistic.h

src/Neuron/neuron.h

src/constants.h