Multilayer Perceptron

Currently the Neural Network in the library has only one hidden layer.
There is need to update neural network model so that it can have multiple layers like other libraries synaptic and brain.js

Start by locating the library’s current neural-network model and reading how it represents its single hidden layer. Compare the relevant multilayer behavior in synaptic and brain.js, then define how multiple hidden layers should be configured and trained. Done means the model supports multiple hidden layers and its behavior is covered by the project’s existing checks, if available.

Written by the indexing model from the issue text.