Port `.npz` weights to TensorFlow and Keras

With a considerable amount of help from Willi Gierke, we were able to port the original .npz weights of new BiT-ResNet models [1] to TensorFlow and Keras.

Colab Notebook showing the porting and all the other details are available here [2]. The converted models are available on TF-Hub as well:

These models are a part of the recent work done by Google Brain on Knowledge Distillation [3].


[1] Big Transfer (BiT): General Visual Representation Learning by Kolesnikov et al.

[2] BiT-jax2tf: https://github.com/sayakpaul/BiT-jax2tf

[3] Knowledge distillation: A good teacher is patient and consistent by Beyer et al.