Implements support for loading and saving GGUF support.

TODO:

• Implement a basic GGUF format loader that loads the file in as a struct.
• Load a Llama model with a remote Hugging Face tokenizer.
  • Load a Llama model with an embedded tokenizer (GGML).
  • Load a Llama model with an embedded tokenizer (HF).
  • Ensure that models with a HF tokenizer can operate without a GGML tokenizer.
• Implement a basic GGUF format saver that saves a Gguf struct to a file.
  • Reimplement quantize. (For extra points, make it multithreaded.)
  • Think about how hyperparameters should generally be treated. Should a model re-write them to a Metadata map?
• Make sure all llm metadata values are used for llama.
• Fix all the models.
  • Fix BLOOM.
  • Fix Falcon.
  • Fix GPT-2.
  • Fix GPT-J.
  • Fix GPT-NeoX.
  • Fix MPT.
• Remove all of the expects.
• Remove the architecture option and load entirely based on the architecture specified in the GGUF.

Open questions:

• Should we still support the old formats?
  • No. Instead, we'll take the old code and build a converter with it. Preferably one that can ingest HF files to provide the necessary information for a fully-compliant GGUF.
• How resilient should we be to malformed GGUF models?
  • Answer: The usual Rust standard. Don't panic if you can avoid it.

Closes #365.