Added NeuronCount and unit test.

Measurement counts the number of neurons an a neural network. It
has the added option of whether to include bias units or not.
Added NNLayerCount and unit test.

It measures the number of layers in a neural network.
Added NNWeightCount and unit test.

Measures the number of weights in a neural network. Can also add a
penalty for activation functions.
Updated Neuron copy constructor to deal with null activation function.
Merge pull request #137 from censlin/nnStructureMeasurements

Neural Network structure measurements.