Add HF integration

[NielsRogge]

This PR makes the model inherit from PyTorchModelHubMixin. This comes with the following benefits:

• download stats
• serialization of weights in safetensors
• automatically inherit from_pretrained and push_to_hub functionalities
• automatic model card.

Hence models can now be loaded as follows:

from models.fractalgen import FractalGen

model = FractalGen.from_pretrained("nielsr/fractalgen-in64")

The model is here for now: https://huggingface.co/nielsr/fractalgen-in64. It is automatically linked to the paper page (which you can claim as an author).

Demo notebook: https://colab.research.google.com/drive/1yHym8o2SYBUdYnUdPFddMlZBQ3aDd78S?usp=sharing.

Would be great if you could try this out and push all FractalGen models to the 🤗 hub!

Fixes #1

[NielsRogge]

See https://huggingface.co/nielsr/fractalgen-in64/blob/main/config.json :)