* Update `no_grad` docs

add alias `paddle.no_grad`
use `paddle.no_grad()` for decorator usage
update code sample

* Fix alias

* Reword decorator usage note

* Add the max, min, maximum, minimum api for the paddle 2.0

update the api doc for the cumsum op 

 Fix the compare ops doc for the api2.0

Fix the argsort, sort the api doc for paddle2.0