Binary classification for multi-class

binary_classification.md

https://stackoverflow.com/questions/42081257/why-binary-crossentropy-and-categorical-crossentropy-give-different-performances

https://stackoverflow.com/questions/45799474/keras-model-evaluate-vs-model-predict-accuracy-difference-in-multi-class-nlp-ta/45834857#45834857

https://stackoverflow.com/questions/44477489/keras-difference-between-categorical-accuracy-and-sparse-categorical-accuracy