Add M2M100 tokenizer (Closes #235) (#250)
* Add `M2M100Tokenizer`
* Allow `added_tokens` list to be empty
* Apply hot-fix for issue in HF's `M2M100Tokenizer`
* Skip M2M100 tokenizer tests for now
TODO: Remove when https://github.com/huggingface/transformers/pull/25478 is merged
* Fix `_build_translation_inputs` for `M2M100Tokenizer`
* Add example code in JSDoc for `TranslationPipeline`
* Update supported_models.py
