We need to provide a way to save and load tokenizers to/from files.
Things that need to be saved:

• Each part (Normalizer, PreTokenizer, ..) and their options
• Added tokens / special tokens
• The model's vocabulary

We can approach this in multiple ways, but in the end, we would like to have a single self-contained file that represents a tokenizer. We will probably need to have some scripts to convert existing models to this new format.