Model storage should support more frameworks/tools

[hhsecond]

Description

stock.model's high level functions such as stock.model.load_weights currently only support PyTorch & Keras models. It needs to support other frameworks such as

• Native TF (<2.0)
• scikit-learn
• ONNX
• TBD

[rlizzo]

Onnx-ML would be good as well.

https://onnx.ai/

[hhsecond]

Thanks Rick. Added ONNX to the list