Standardize MNIST dataset.
remove old data prep file.
Correct doc string.
rename sigmoid to logistic
add output_functions.py file
add file that contains output function, cost function, and cost function
derivatives.
add a getter function in the output_functions module.
Add softmax output and NLL cost, use tanh activations. Implement a better
random initializer module.
Refactored the feedfwd_neural_network class
refactor code to allow hooks for getting distributions after each iteration.
modified makefile.