ADD BORT

[stefan-it]

Hi,

this is a "clean" follow-up PR to the first attempt of adding Bort to Transformers (see #9112).

As Bort is based on the BERT architecture, there's no need to define own model classes, such as BortModel. This is done in the main Bort configuration via:

"model_type": "bert"

Bort uses the same vocab as RoBERTa, so the tokenizer instance is also configured in the model configuration:

"tokenizer_class": "RobertaTokenizer"

Basic integration tests and a (hopefully verbose) conversion script are also included in this PR.

[patrickvonplaten]

Awesome! And good timing as well - adding the 40th model architecture when stars hit 40K!

[LysandreJik]

This is really great. The integration tests are a fantastic addition, too. Thanks for taking care of it @stefan-it, and congrats for adding the 40th model to Transformers 😄

[sgugger]

Thanks for adding this new model! When referencing other pages in the documentation, it's better to use :doc: instead of a hard link, as it will then work in all versions of the documentation (which don't have the same base url).

[patrickvonplaten]

Thanks for adding this new model! When referencing other pages in the documentation, it's better to use :doc: instead of a hard link, as it will then work in all versions of the documentation (which don't have the same base url).

Sorry that was my bad! I copied it from DialoGPT -> Updated it there as well

[sgugger]

Ah sorry @patrickvonplaten, the model_doc/ should be removed are the pages are in the same folder. That should resolve the build doc error.

[patrickvonplaten]

Great job @stefan-it