* update 2.0 public api in nn

* replace Chinese character cause error in ci;synchronization with pr:#32588 to avoid 'ascii' codec in python2

* numbers used in paddle.nn.functional.norm but not imported

* fixed docs.

* Fixed docs. test=document_fix

code bak.

fixed docs. test=document_fix

* Revert to previous version of python/paddle/fluid/backward.py

* fixed bugs.

* test=document_fix. Fixed examples.

* fix cross_entropy calculation error

* add unittest and fix static

* Support list and tuple for parameters of layer_norm, multiprocess_reader, DatasetFolder and ImageFolder.

* add unittest for layer_norm.

* add require gpu for example.

This reverts commit 4b7242b0.

* add sendrecv, test=develop

* optimize pull sparse

* optimize pull sparse

* change macro

* format

* fix bn docs

* fix unittest

* Modified params of some APIs to support tuple and list.

* fixed bug.

* Modified the return value of tensor.grad from numpy as tensor.

* Modify unittests.

* fixed bugs.

* Add warning info for x.grad

* fixed unittests which used x.grad

* fixed bug.

* fix dataloader exit error if user exit program when dataloader is still iterating. test=develop

* Unset ReserveSpace for inference program.

* Support training from an inference program.

* change prepend to append

* fix ut

* add testcase

* fix ut

* fix test_custom_relu_model

* fix model parallel

* rm parallel_help.py

* add embedding

* support backward return None.

* edit unittest.

* edit code according to CI

* Improve error information

* skip op has no fp16 kernel

* add ut

paddle.to_tensor will be translated to paddle.assign in Dy2stat, however paddle.assign doesn't support int, float, bool. This PR added the supports.

* add pp dygraph, test=develop

* Dygraph reocmpute

* unitest for Dygraph reocmpute

* dy recompute remove unitest for win and mac

`range` API set its output shape in dygraph but not in static graph, which can cause Dy2stat error. This PR set the shape of `range` API when possible.

* support save/load binary format tensor

* Fix error when create cudaplace

* Fix error when create cudaplace

* Fix error when create cudaplace

* get devive context from pool.

* move define of 'SerializeToStream' and 'DeserializeFromStream' to 'lod_tensor.cc' and 'selected_rows.cc'.

* support complex object

* improve coverage.

* improve coverage

* improve coverage.

* fix a bug.

* polish API

* save/load program

* paddle.save/load: layer

* deal with conflict

* if PY2, block test_paddle_save_load.TestSaveLoadLayer

* polish code.

* polish code

* edit unnittest

* The condition for object to be identified as state_dict becomes strict

* use 'core._cuda_synchronize'

* add pipeline layer

* update

* fix bug: when x.dim < y.dim, the result of compare_op is inverse to expected result

* support the cuda for fix the compare broadcast bug

* fix tc trt shape

* fix fc dynamic shape

* add fc shape assert

* update

* let paddle.utils.install_check support CPU package with GPU device

* use use_cuda in dygraph checking

* add unittest for install_check