Image & Audio formatting for numpy/torch/tf/jax
Added support for image and audio formatting for numpy, torch, tf and jax.

For images, the dtype used is the one of the image (the one returned by PIL.Image), e.g. uint8

I also added support for string, binary and None types. In particular for torch and jax, strings are kept unchanged (previously it was returning an error because you can't create a tensor of strings)