Add RegNet models and weights

[rwightman]

No description provided.

[Kshitij09]

@rwightman when I'd be able to try RegNets ? I tried building from sources but wasn't able to import this model.

Also, there's some error with SkResnext models, something related to dimension mismatch. Will report that later.

[rwightman]

They're definitely on the master, and the skresnext was tested with a full validation.

timm.create_model('regnetx_064', pretrained=True) as an example of one...

Remove any other versions of timm in your conda/pip environment, and that there is no old timm folder in whatever directory you are working from. Then try re-install from source.

I have not updated pip package but you can install master with pip install git+https://https://github.com/rwightman/pytorch-image-models or run setup.py or pip install . from a local checkout