* update dygraph user guide to fit new api

* refine doc

* remove pylayer support doc

* refine words

* refine sample code

* Add usage manual for VisualDL
The usage manual will be helpful for beginners to make use of VisualDL.

Components of VisualDL are introduced in details, including:
	* Definition of Functions
	* Parameters explanation
	* Demo program for each component

* add_index

* refine inference api

test=develop

* fix typo

* fix typo

* fix comments

* TRT预测库仅支持GPU编译

DLTP-739 完善tensorRT使用文档 TRT需要GPU编译

* DLTP-965 预测模型的保存和加载文档优化

* Windows_installation_English

* DLTP-1417 受训改为训练

* 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

* add flag files

* add flags file

* delete space

* 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

* add python inference api doc

* Polish executor doc

* split layers,test=develop

* split nn layers

* remove nn header, test=develop

* new python op doc,test=develop

* fix typo, test=develop

* modified lrn formula

* modified design idea

* Update fluid_design_idea.md

* Update fluid_design_idea.md

* add contribute faq

* refine with comments

* Add the description of the quantization-aware training model format.

* add the abstract.

* Add lod specs

* Update op notes

* Update lod specs

* add infer shape

* fix bug

* fix example; test=develop

* fix language; test=develop

* fix format error

* fix error

* fix error

* update en api doc

* update Paddle commitid

This reverts commit 76d8f574.

* update_faq

* revise the style

* modify the FAQ format

* update_releasenote_0428

* add new

* update_commitid_Paddle_0428

* run gen_doc

* fix_table_link

* fix en

* fix typo

* Update native_infer.md