Adaptive Attention Span for Transformers
# 🌟New model addition

## Model description

<!-- Important information -->

## Open Source status

* [x] the model implementation is available: https://github.com/facebookresearch/adaptive-span
* [x] the model weights are available: get_pretrained.sh
* [x] who are the authors: Facebook Research

## Additional context

No additional dependencies required.

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
<|||||>Any clue about how to integrate that into a BERT model?