Reference:
Neural Network from scratch: https://github.com/dennybritz/nn-from-scratch/blob/master/nn-from-scratch.ipynb
Computational Graphs for Backpropagation: http://colah.github.io/posts/2015-08-Backprop/
Matrix Multiplication for Backpropagation: https://cs231n.github.io/optimization-2/
Softmax-Crossentropy derivatives: https://deepnotes.io/softmax-crossentropy