* fix is_empty api and code example; test=develop

* remove inplace argument

* fix sample code

* fix sample code

1. fix a bug that paddle.nn.RNN does not initialize the state for the cell correctly;
2. add unittest for paddle.nn.RNN and paddle.nn.BiRNN

* modified sample code of add_position_encoding to  2.0, test=document_fix

* use core.op in add_position_encoding API.

* add test for add_position_encoding in dygraph mode

* fix example code

* rename var to tensor

* remove static

* fix return type

* add float64 input to ctc_loss

* modified error message of  warpctc

* update repo and tag of warpctc

* add test for warpctc with float64 input

* modified warpctc.cmake to make sure build always

* resolved sample code bug of warpctc

* add core.ops in warpctc dygraph

* fix a bug of test

* Fix example code of api `fluid.layers.switch_case` to use api2.0

* delete `paddle.nn.switch_case` alias and add `paddle.static.nn.switch_case`

* Fix example code of api fluid.layers.case

* delete paddle.nn.case alias and add paddle.static.nn.case

* add static check on data()

* follow comments

* fix ut

* Makes the Bind Method more intelligent

* Makes the Bind Method more intelligent

* fix unittest

* fix unittest

* fix conflict

* add double grad compute for batch norm,test=develop

* fix unittest, test=develop

* remove unuse tensor,test=develop

* add format,test=develop

* update, test=develop

and optimize the c++ implmentation of empty op as PR#26659 reviews,
and add bool for shape op.

* enhance collect_op for dygraph, test=develop

* enhance detection ops with lod, test=develop

* support none bbox left in generate_proposals, test=develop

* unfiy MultiLevelRoisNum, test=develop

* update core.ops, test=develop

* add op register for new input & output, test=develop

* delate some wrong message test=develop, test=document_fix

* delate some wrong message

* fix unsqueeze in dygraph

* add test

* add test

update doc of paddle.to_tensor

* refine paddle.stack

* support TensorArray

* add test

* fix coverage problem

* fix coverage problem

* fix sample code

As the title

* add embedding 2.0

* add embedding support input int32

* set default dtype for distribution API

* Add unittest

* Add unittest

* fix import get_default_dtype problem

* delete change under fluid.layers.nn

* little change

* add deprecated, test=develop

add broadcast feature for elementwise logical op

* 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>

* update doc, test=document_fix

* add attr(dtype)

* refine code

As the title.
Co-authored-by: Nwujionghao <wujionghao@email.com>

* add div, floor_div, remainder