Pre-release for Transformers.js v2.0.0

Major changes

• Complete ES6 rewrite
• Documentation live at https://huggingface.co/docs/transformers.js
• Overhauled testing framework (now using Jest)
• Improve hub integration (now you can simply pass model ids to pipeline, AutoModel, AutoTokenizer, and AutoProcessor.)
• Node.js model caching (#62)

Minor changes

• Added tutorials and example projects (https://github.com/xenova/transformers.js/tree/main/examples)
• CI/CD with GitHub actions
• Various bug fixes and improvements