v1.3.0

Trax now has docs on - https://trax-ml.readthedocs.io/en/latest/trax.html thanks to @j2i2 !

Many usability changes, especially in trax.supervised.training.TrainTask/EvalTask/Loop, docs, comments etc.

• flat saved model/checkpoint representation
• lr schedule simplified, now they just take step number.
• configs are now in supervised/configs and rl/configs.
• RL obsolete code cleanup.

Also rapid development of the tf-numpy codebase !