* add_api_cn (#437)

* add gpu benchmark page (#436)

* add gpu benchmark

* fix comments

* add chinese link in gen_doc.py (#439)

* modified gen_doc.py

* Update gen_doc.py

* update gen_doc.py

* Update mobile doc (#440)

* update_en_structure

* update_Paddle_commitid

* delete_DS

* update_mobile_doc

* Update book commit (#438)

* update_en_structure

* update_Paddle_commitid

* delete_DS

* update_book_commit_id

* update_api_rst

* Adjust structure of advanced usage (#442)

* adjust_structure_of_advanced_usage

* Update paddle_gpu_benchmark.md

* adjust_toctree_hidden

* fix_api_guide

* Update index.rst

* fix deadlinkes (#443)

* add_toctree (#445)

* adjust_beginners_structure (#446)

* adjust_beginners_structure

* Update index.rst

* update install_doc for python3 (#418)

* update install_doc for python3

* update python3.5+ info,test=develop

* fix review, test=develop

* fix_pic (#447)

* update_en_structure

* remove doc/fluid/api/.DS_Store

* add async_training.rst

* add cpu_train_best_practice.rst

* clean code

* add doc for large_scale_sparse_feature_training

* add index for distribute train api guide

* follow_comments

* fix_link_format

* fix_link_format

* follow_comments_large_scale

* follow_comments

fix https://github.com/PaddlePaddle/FluidDoc/pull/400#discussion_r237335307

Add sparse update API guide.