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* Start doc tokenizers

* Tokenizer documentation

* Start doc tokenizers

* Tokenizer documentation

* Formatting after rebase

* Formatting after merge

* Update docs/source/main_classes/tokenizer.rst
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>

* Address comment

* Update src/transformers/tokenization_utils_base.py
Co-authored-by: Thomas Wolf <thomwolf@users.noreply.github.com>

* Address Thom's comments
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
Co-authored-by: Thomas Wolf <thomwolf@users.noreply.github.com>