Resume from the latest pickle

[woctezuma]

Hello,

I know you don't accept pull requests. However, this could be of interest to others who want to run the code on Google Colab,

To put it in a nutshell, I have ported my changes from NVlabs/stylegan2-ada#6 Namely:

• save output images as JPG,
• automatically resume from the latest .pkl file with the command-line argument --resume=latest,
• automatically set the resume value of kimg,
• allow to manually set the resume value of the augmentation strength,
• add config auto_norp to replicate the auto config without EMA rampup,
• allow to override mapping net depth with the command-line argument --cfg_map,
• allow to enforce CIFAR-specific architecture tuning with the command-line argument --cifar_tune.

[woctezuma]

I made the pull request with the wrong branch. The correct branch should not have been main but google-colab. Done with #3.