add gelu into document index (for both english and chinese doc)

* Add Chinese Doc for cond API

* add Chinese document of control flow API case and switch_case. test=develop

* polish TypeError according to reviews. test=develop

As the title

* add masked_select api chinese document

* refine, test=document_preview

* fix-apis-develop

* fix-one-error

* remove Fake and fix layers_cn.rst

* fix-apis-develop

* fix-one-error

fix-contents_cn

* 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.

* add new seq2seq api_cn, test=document_preview

* add seq2seq api_cn, test=document_preview

* add seq2seq api_cn, test=document_preview

* add instance norm

* add strided_slice op cn doc test=develop

* fix typo test=develop

* fix typo test=develop

* fix typo test=develop

* fix typo test=develop

* fix typo test=develop

* fix typo test=develop

* fix according review  test=develop

* fix according review  test=develop

* fix according review  test=develop

* fix gather_nd scatter_nd_add scatter_nd, test=develop

* fix centerloss, test=develop

* fix the description, test=develop

* fix the doc, test=develop

* refine doc for api Program, BackwardStrategy, default_start_up_program

* remove wrong binary char to make file not binary

* delete binary file and push a new file as regular one

* change name back since we delete bianry Program_cn on develop

* refine clone doc

* remove additional gitignore

* refine doc about some info

* refine doc about some info

* refine doc about some info

* refine doc about some info

* refine doc about some info

* remove useless info

* refine doc

* fix code

* fix doc error in Program_cn.rst

*  add code and refine doc

* refine clone doc

add cn doc for crop_tensor
modified cn doc for crop

* fixed one error of http://newicafe.baidu.com/issue/DLTP-2186/show

* update api_cn of develop

* fixed some errors of http://newicafe.baidu.com/issue/DLTP-2129/show

* fixed one error of api_cn

* fixed some errors of api_cn

* fixed some errors of api_cn

* fixed two errors.

* fixed two errors

* fixed one error.

* fixed one error

* fixed one error.

* fixed two errors.

* fixed one error.

* fixed two errors

* fixed two links

* synchronize api_cn with the api_en of develop.

* updated develop/api_cn

* update the api_cn of develop

* update api_cn of develop

* fixed some errors

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* fixed some wrong links

* fixed two links

* fixed two links and some error.

* fixed some errors.

* fixed two links

* break up layers and change index of layers

* prettify script

* update api_cn; fix the error of reverting layers_cn to 1.4; include previous changes

* update layers_cn; add code example to elementwise_mod

* delete recordio_writer_cn; revert index_cn

* update api_cn after review

* fix io_cn.rst

* update layers_cn

* update io_cn

* modify write_docs_cn, write_docs_en, include specifications about python 2.7.15 and creating  virtual env with conda

* gitignore update

* revert .gitignore;  update write_docs

* icafe DLTP-1328, stress  exe.close()

* DLTP-1383 不可迭代更正

* DLTP-1404 修复动态图文档中每段代码的格式和大小都不一样

* DLTP-1390 Pyreader中文显示格式问题

* DLTP-1393 无效链接

* DLTP-1421 paddle.fluid.layers.reduce_max中文翻译有问题

* DyGraph 调整标签结构

* api modification

half modification of fluid/io/layers

* Apply suggestions from code review
Co-Authored-By: Nzy0531 <48094155+zy0531@users.noreply.github.com>

* Update fluid_cn.rst

* 1.3 => develop (4.12)

* Delete InMemoryDataSet and QueueDataSet 

refer to #784

* add pixel shuffle and in_dygraph_mode

* api_trans_0410

* Update io_cn.rst

* Apply suggestions from code review

* fix bugs