* Update docs for `abs` `acos` `asin` `atan` `ceil` `cos`

update code samples
`Variable` -> `Tensor`
remove activation wording
explain cos input/output range
misc fixes

* Apply input template

* Update `enable_imperative` -> `disable_static`

* 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

* remove the out args

* update log docs

* update log1p docs

* test add api

* add_api test=develop

update the margin rank loss api doc

fix unstack cn doc

update demo code in NLLLoss_cn.rst

* add pairwise distance cn docs

* fix link

* add alias

* refine format

* fix doc tree

* fix format

* add name

* change out -> output

* change eps -> epsilon

* fix name

Update the docs of nn.loss.L1Loss and nn.functional.l1_loss

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

* fix MSELoss ch doc

* support pact demo load checkpoints

* fix example code

* add two args

* fix args

* change num_filters test=develop

update the api doc for the cumsum op 

* fix wrong in doc

* fix docs math style

* fix docs

* fix conv2d

* fix conv2d

update the sort api, delete the unused index output

* add_three_args

* add broadcasting index and some common args text=develop

* fix broadcasting index test=develop

* fix broadcasting test=develop

As the title.

* Add fluid.rst

* fix cn rst

LGTM