[WIP] Add early stopping to the trainer
closes #4894 
Well that was quick. Awesome! Let me know if you need some help (for the pytorch part) or code review.<|||||>Looks like a duplicate of https://github.com/huggingface/transformers/pull/4186<|||||>> Looks like a duplicate of #4186

You are absolutely right. Closing this in favour of https://github.com/huggingface/transformers/pull/4186