Implement MaxPool operator

[Swopper050]

ONNX operator: https://github.com/onnx/onnx/blob/master/docs/Operators.md#MaxPool

Gorgonia operators:

https://pkg.go.dev/gorgonia.org/gorgonia#MaxPool1D

https://pkg.go.dev/gorgonia.org/gorgonia#MaxPool2D