* support data_norm_op run in CUDA
* add two parameters sync_stats & summary_decay_rate
* add UT

* add the framework support for distfc and ut, test=develop
* fix the implementation of shard_index_op, test=develop

* fix the fill_constant op precious problem test=develop

pass the argument `allow_out_of_range` of one_hot op to c++ back end.

* add input type and input data type check for Print_op test=develop

* add control flow API: case. test=develop

* delete 'raise TypeError' in _error_message() and return a string. test=develop

* polish API document. test=develop

* fix auc drop first commit test=develop

* update datanorm op

* update datanorm with enforce test=develop

* update test=develop

* update format test=develop

* update format

* update format test=develop

* add unit test test=develop

* update unit test test=develop

* update format test=develop

* update format test=develop

* update API description test=develop

* update API description test=develop

* update format test=develop

* fix codes as comments test=develop

* fix description as comments test=develop

* fix description as comments test=develop

* update codes.. test=develop

* modified error message for conv and conv_transpose, test=develop

* modified doc of conv and conv_transpose op, test=develop

* modified the expression for error message, test=develop

* modified error message for group_norm op, test=develop

* modified detail of Attr(data_format) or Attr(data_layout)

* add ValueError in API doc for maxout op, test=develop

* add API switch_case. test=develop

add Nest

* modify code according to reviews:
1.Attr(branch_index) support 'uint8' and 'int64' besides 'int32'.
2.remove useless code.
test=develop

* replace fluid.layers.data with fluid.data and polish API document. test=develop

* add input type and dtype check template, and update some APIs check

* refine check template, and update some APIs check in nn.py

* update some APIs check in loss.py

test=develop

* 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