* update the demo code and the doc of varbase.backward.

* update the doc of the fake interface `paddle.fluid.Variable`.

* remove BackwardStrategy.

fix bug that can't print int8_t 

* Add RNN related apis in paddl.nn
test=develop

* new rnn api, cell almost done

* add new progresses in rnn APIs for 2.0

* refine rnn APIs and docstrings.

* add unittets

* disable gpu tests when paddle is not compiled with cuda support

* remove unnecessary imports

* fix docstring

* add to no_sample wlist

* backport to python2 to avoid yield from

* add **kwargs, fix typos

* update docstrings for birnn

* rename argument for SimpleRNN and SimpleRNNCell, fix sample code

* add default value for initial_states in fluid.layers.birnn
Co-authored-by: Nguosheng <guosheng@baidu.com>

As the title

* Add the option to execute unit tests only at night

* set ut nightly label for 3 cases.

* add InputSpec

* add unittest for tensorSpec and SimpleNet

* add intepolte_v2

* fix linear interp

* polish unittest, test=develop

* update code samples to 2.0 API, test=develop

* remove warning, test_develop

* add name in attrs, test=develop

* polish code, test=develop

* change Align to align, test=develop

* fix unittest in py3,test=develop

* fix coverage, test=develop

* fix coverage, test=develop

* fix for windows ci, test=develop

* fix coverage, test=develop

* Update Paddle-Lite commit hash.

* Add BF16 data type to VarTyp protobuf message.

* update doc, test=document_fix

* add attr(dtype)

* refine code

* API2.0 del old api(BilinearTensorProduct) from nn init.py, test=develop

* add import for deprecated, test=develop

* modify deprecated location, test=develop

* fix english doc, test=develop

* Update __init__.py

* Update __init__.py

* Update common.py

* fix english doc, test=develop
Co-authored-by: NChen Weihang <chenweihang@baidu.com>

* add TensorDataset. test=develop

* modified timeout value on windows and mac (#26690)

* add Local SGD algorithm referenced paper
test=develop

add collective op for cpu using gloo and paddle.distributed.* apis

* add gen_alias_mapping.sh

* fix problems commented by Lutao

* rename _to_variable to _to_tensor

* fix unittest coverage

* little problem

* fix the tanh

* fix the learning rate

test=develop

* Fix pip2 opencv-python version

* opencv-python==4.2.0.32

* fix whell version

* fix doc of lr_scheduler

* fix doc

add the top v2 for the paddlepaddle api 2.0

test=develop