This code is directly learned from neural network youtube series by sent dex
Important Links https://www.youtube.com/watch?v=Wo5dMEP_BbI&list=PLQVvvaa0QuDcjD5BAw2DxE6OF2tius3V3
Back-Propagation is very simple. Who made it Complicated ? https://medium.com/@14prakash/back-propagation-is-very-simple-who-made-it-complicated-97b794c97e5c