* polish en doc of data_loader

* follow comments

* use fluid.data()

* update cosine decay, test=develop

* update, test=document_fix

* update, test=document_fix

* update, test=document_fix

* update, test=document_fix

* update, test=document_fix

* update, test=document_fix

* 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

* refine build and install tutorial doc for paddle inference

* remove trt_benchamrk after merge it to trt doc

update sequence_softmax_cn.rst

* add astype api in Variable and refine code style

* add astype api in Variable and refine code style

* add astype api in Variable and refine code style

* refine doc

* polish cn document of unique_name

* polish guard and switch

* add example code

* add filter to simplify optimizer api doc

* update related optimizer doc

* refine prepare steps doc, test=develop

* replace layers.data with fluid.data, test=develop

* update softmax_cn.rst, test=develop

* update softmax_cn.rst, test=develop

* fix error, test=develop

* add comment for name, test=develop

* update softmax_cn.rst, test=develop

* update softmax_cn.rst, test=develop

* fix softmax_cn.rst, test=develop

* fix softmax_cn.rst, test=develop

* polish model average zh doc api

* polish details

* polish based review commment

* fix indent

* fix the doc format of io.chain.

test=develop
test=document_preview

* fix fluid.data code example, test=develop, test=document_preview

* skip PipeReader in IO

* skip PipeReader in IO
test=develop

* fixed bugs about PipeReader

change fluid.layers.data to fluid.data in api_cn for retinanet_target_assign, sigmoid_focal_loss, retinanet_detection_output. (#1473)

* test=document_preview
change  to  in api_cn for retinanet_target_assign, sigmoid_focal_loss, retinanet_detection_output.

* test=document_preview
remove Notice: this OP supports CPU mode only in api_cn for retinanet_target_assign and retinanet_detection_output

* fix DataFeedDesc set_batch_size, set_dense_slots cn api doc test=document_preview

* fix continuous_value_model op cn doc

* fix some rst error

* add cpu support only in cvm op

* add explain of N in cvm

* refine lstm

* refine LSTMs, test=develop

* fix notice color, test=develop

fix the API doc of paddle.fluid.layers.array_length

* fix the document of API:fluid.Layers.array_length

* fix the document of API:fluid.Layers.array_length

fix the document of API:fluid.Layers.array_read

* fix the document of API:fluid.Layers.array_read

* fix the document of API:fluid.Layers.array_read

fix the API doc of paddle.fluid.layers.array_write

* fix the document of API:fluid.Layers.array_write

* fix the document of API:fluid.Layers.array_write

* fix the document of API:fluid.Layers.array_write

* fix the document of API:fluid.Layers.array_write

* doc fix

* update doc/fluid/api_cn/layers_cn/add_position_encoding_cn.rst
update doc/fluid/api_cn/layers_cn/beam_search_cn.rst
update doc/fluid/api_cn/layers_cn/beam_search_decode_cn.rst
update doc/fluid/api_cn/layers_cn/chunk_eval_cn.rst
update doc/fluid/api_cn/layers_cn/dynamic_gru_cn.rst
update doc/fluid/api_cn/layers_cn/gru_unit_cn.rst
update doc/fluid/api_cn/layers_cn/lstm_unit_cn.rst
update doc/fluid/api_cn/nets_cn/scaled_dot_product_attention_cn.rst

* Update format for dynamic_gru_cn, gru_unit_cn and scaled_dot_product_attention_cn.