[0.12.0]

The breaking change was causing more issues upstream in transformers than anticipated: https://github.com/huggingface/transformers/pull/16537#issuecomment-1085682657

The decision was to rollback on that breaking change, and figure out a different way later to do this modification

Bump minor version because of a breaking change. Using 0.12 to match other bindings.

• [#938] Breaking change. Decoder trait is modified to be composable. This is only breaking if you are using decoders on their own. tokenizers should be error free.

• [#939] Making the regex in ByteLevel pre_tokenizer optional (necessary for BigScience)

• [#952] Fixed the vocabulary size of UnigramTrainer output (to respect added tokens)

• [#954] Fixed not being able to save vocabularies with holes in vocab (ConvBert). Yell warnings instead, but stop panicking.

• [#961] Added link for Ruby port of tokenizers