* Split some APIs from nn.py to loss.py

test=develop

* fix test_detection unit-test

test=develop

* set the default value of alpha for prelu to 0.25, test=develop

* add the call to __syncthreads(), test=develop

* fix the implementation of cpu prelu, test=develop

* repair the implementation of element mode prelu, test=develop

* modify test_prelu_op.py, test=develop

* split some APIs from nn.py to rnn.py

* split some APIs from nn.py to sequence_lod.py

test=develop

* fix unit-test bug

test=develop

* fix test_layers unit-test bug

test=develop

These ops are useful in control flow.

* fix uniform random; test=develop

* add uniform random test; test=develop

test=develop

* maxout support channel_last input, test=develop

* modified details of Input(X) and Attr(groups, axis) in doc, test=develop

support Tensor for split and concat, support -1 in num_or_sections, add check num_or_sections (#20780)

* improve split and concat op:
1. support Tensor for argument 'dim' in split op.
2. support Tensor for argument 'axis' in concat op.
test=develop

* redefine function GetDataFromTensor and set unknown output shape to - 1.
test=develop

* add check: Attr(sections) match Input(X). test=develop

* support Tensor for attr(sections) and attr(sections) can contain -1.
add check for attr(sections).
test=develop

* modify error message for concat and call Resize only when necessary. test=develop

* improve unsqueeze op to support int, Tensor and Tensor list for argument axes.
test=develop

* call Resize only when necessary. test=develop

*  Make shape tensor support int32

* All elements in attr(shape) of crop_tensor can be -1, test=develop, test=document_preview

* fix the bug that attr(offsets) should be initialized, test=develop

* refine Categorical and MultivariateNormalDiag en doc test=develop, test=document_fix

* refine Categorical and MultivariateNormalDiag en doc test=develop, test=document_fix

* update the infer shape of matmul,  test=release/1.6

* add unittests of matmul, test=release/1.6

* change func names, test=develop

* fix elementwise_floordiv_op and elementwise_mod_op, test=develop

* fix API.spec, test=develop

* fix API.spec, test=develop

* fix error message for elementwise_add/mul;test=develop

* fix type error message;test=develop

* add data type check, test=develop

* polish error messages, test=develop

* polish error messages, test=develop

* Remove support for the CPU architecture matmul, test=develop

* fix syntax bug, test=develop

* add input type and dtype check for cast_op
test=develop

* fix annotation
test=develop

* support more data type

test=develop

* fix bug for fill_constant's error type

test=develop

* improve converage

test=develop

* improve converage

test=develop

test=develop

* add expand_as op, test=develop

* add expand_as op,test=develop

* add expand_as op,test=develop

* add nn.py, test=develop

* delele paddle_enforce, test=develop

* refine py_reader exit, test=develop

* fix multiprocess_reader exception unittest, test=develop

* increase code coverage for legacy fluid.layers.py_reader, test=develop

* Fix docs of gru_unit and dynamic_gru.

Fix basic_gru in rnn_impl.py.

Add error messages for param_attr setting in layer_norm api.

Add int64 dtype for expand.

test=develop

* Reopen unit-tests of basic_gru/basic_lstm in rnn_impl.py.
test=develop

* Add unit test for layer_norm api.
test=develop

* Remove the deprecated gru doc fix. test=develop

* Fix basic_gru test coverage. test=develop

* Update API.spec. test=develop

* Update API.spec. test=develop

* Fix test_basic_gru coverage test. test=develop

* Update test_basic_gru in test_layers to use fluid.data
test=develop

* Update test_basic_gru for coverage. test=develop

* Refine error message of transpose.
* Fix transpose, multiplex, unsqueeze, unstack. test=develop, test=document_preview, test=document_fix

* fix the error message of zeros op
test=develop

* Fix unittest of zeros op
test=develop

2. fix bug in backward.py: using fill_constant instead of fill_constant_batch_size_like
3. fix bug in ExpandGradOp.

test=develop

* Fix the assign data check. test=develop

* Fix test_assign_op.py. test=develop

* disable nccl test

* Update version.

* fix term core only

* fix transpiler error

* fix protobuf memory leak (#11177)

fix protobuf memory leak

* "change eigen mirror"

* refine en doc sequence enum pad expand mask d2s

* refine seq enum expand mask pad test=develop, test=document_fix

* remove cn char test=document_fix

* spec test=document_fix

* code style test=document_fix

* test=document_fix

* test=document_fix

* test=document_fix

* test=document_fix

* test=document_fix

* test=document_fix

* Refine the documentation of sums.

* Remove Chinese comments and update API.spec.

* Refine the description of input argument.

* Update API.spec.
test=develop
test=document_fix