feat: add cli for tokenizer and training

[b00f]

This PR adds CLI with two subcommands:

1. Tokenize: To tokenize a text using a given model
2. Train: To train a new tokenize model

[Narsil]

If it's that small, and adds new dependencies, I feel like it should be it's own crate. tokenizers is a library, it shouldn't be a CLI as well.

[b00f]

If it's that small, and adds new dependencies, I feel like it should be it's own crate. tokenizers is a library, it shouldn't be a CLI as well.

This is a valid point... I am not sure if we can define bin dependencies separately.

[ArthurZucker]

We can do a new crate just fort the CLI, it does make sense instead. If this is highly requested happy to do!