ONNX support.

[MuhammedSaleem-Brej]

I hope to add ONNX format support to this excellent framework.
ONNX is an open-source and a standard format of AI models.
With ONNX we will be able to share our models between frameworks and programing languages.

[haifengl]

You are more than welcome to contribute to this project! I believe that there is already a Java binding for ONNX. Can you please share what you would like to develop? Thanks!

[MuhammedSaleem-Brej]

Firstly, thank you very much for your generosity
And secondly I aim to make Smile framework able to import and export ONNX models using smile.io package.
The next virtual code may explain the idea.
import java.nio.file.Path;
import smile.classification.RandomForest;
import smile.io.Read;
import smile.io.Write;
// Import an ONNX model.
RandomForest model = (RandomForest) Read.onnx("/home/model.onnx");
// Export an ONNX model.
Write.onnx(model, Path.of("/home/model.onnx"));

[haifengl]

Cool. Feel free to create PR when you get it work. Thanks in advance!