Add the description and example of shape tensor supporting int32

* fix Layer and Pool2D api, test=develop

* update label_smooth_cn.rst, test=develop

* Polish cn doc fo gru_unit, lstm_unit and scaled_dot_product_attention.

* Add gather_tree_cn.rst and update the data type of assign/fill_constant_batch_size_like/gather_nd.

* Fix _cn_api_fluid_layers_gather_tree

* Update tensor_array_to_tensor and add mse_loss.

* fix Layer and Pool2D api, test=develop

* update label_smooth_cn.rst, test=develop

* add new seq2seq api_cn, test=document_preview

* add seq2seq api_cn, test=document_preview

* add seq2seq api_cn, test=document_preview

modify fluid.layers.data to fluid.data and Synchronize Chinese doc and English doc

Fix fluid.layers.data of example code, Synchronize Chinese and English DOC of API:layers.sum.

* Refine the Chinese documentation of DynamicRNN.
test=develop
test=document_preview

* Refine the memory interface of DynamicRNN.
test=develop
test=document_preview

* Refine update_memory and output of DynamicRNN.
test=develop
test=document_preview

* Update the format of note and fix a error in example.
test=document_preview

* Add name and correct some examples.

* Refine the documentation according to the review comments.

* Add function list and the doc of function __call__.

* Add optional for x in step_input.
test=develop

* Update sub-titles.

* Change fluid.layers.data in examples to fluid.data.

* Add examples for step and static input.
test=develop

* Refine some sentences.
test=develop

* Add description of shape and data type for input and output variables.
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test=develop

* fix sequence_enumerate cn doc

* only surpport LoDTensor

* add input output shape

* test=document_fix

* fix space_to_depth cn doc

* change name's text

* add input output shape

* add code example

* test=document_fix

* revision

* change name's text

* add input output shape

* test=document_fix

* update smooth, test=document_fix

* update, test=develop

* update, test=document_fix

* update, test=document_fix

* update, test=document_fix

* update, test=document_fix

* fix example code format, test=document_fix

* fix sequence_pad cn doc

* add input output shape

* fix length info

* fix length info and pad_value info

* test=document_fix

* revision sequence_expand cn doc

* only surpport LoDTensor

* change name's text

* add input output shape

* add code example

* add code example

* test=document_fix

* fix sequence_expand_as cn doc

* only surpport LoDTensor

* add input output shape

* add code example

* add code example

* test=document_fix

change the output of retinanet_target_assign in api_cn

* update cn doc for create_py_reader_by_data

* refine decription and sample code for create_py_reader_by_data

* replace fluid.layers.data with fluid.data in the sample code of cn doc of create_py_reader_by_data op

* refine the description of capacity of create_py_reader_by_data

* fix description for create_global_var,create_parameter test=develop test=document_fix

update example code, use fluid.data swish, gaussian_random, thresholded_relu, test=document_preview (#1487)

* fix example for thresholded relu, test=document_preview

* update example code for swish, thresholded_relu, gaussian_random in chinese doc, test=document_preview

* fix example code for thresholded_relu, test=document_preview

* fix ref for name, test=document_preview

updates sequence_scatter_cn.rst 

updates sequence_unpad_cn.rst

update sequence_softmax_cn.rst