

TITLE
Improve coverage of the documentation

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6

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Currently, some public classes are not documented anywhere because we didn't create the corresponding doc pages. Those missing pages are:

- Benchmark classes
- Bert Japanese
- Data collators

If someone feels like working on one of those, please tag yourself with a comment on this issue. Once the objects are properly documented, they can be removed from the `SHOULD_BE_DOCUMENTED` constant in [this file](https://github.com/huggingface/transformers/blob/1310e1a758edc8e89ec363db76863c771fbeb1de/utils/check_repo.py#L374).
