* Update link in training_best_practice.
test=develop

* Update the documentation.
test=develop

* Refine the format.
test=develop

* Change the format of title.
test=develop

* update_user_guides&&release_notes,test=develop

* update_user_guides,test=develop

* fix Fluid Doc deploy elastic ctr on baidu cloud, image deadlink error test=develop

* remove dead link

* update feeding_data.rst, test=develop

* poish description, test=develop

* fix data shape, test=develop

* Update machine translation in book for 1.7

* Update index.cn.html in machine translate

* Updata the format errors of machine translation in book for 1.7

* Small fix of print in machine translation in book.

fix typo of conda doc 

remove redundant index item

remove Tracer in release/1.7 en doc

add API tag for en docs

* rewrite c api cn doc,, test=develop

* fix some mistakes, test=develop

* refine the doc, test=develop

* refine c api lod information, test=develop

* fix shuru to shuchu in comment, test=develop

upgrade api for rec_case

[Cherry-pick #1810] Update doc 'programming_guide.md', using new control flow APIs as example (#1815)

Update doc 'programming_guide.md', using new control flow APIs as example, see #1810 for details

* update cpu distribute practice

update fluid.layers.data to layers.data

* update install doc for 1.7.0, test=develop

* update table.md, test=develop

* fix cuda support, test=develop

update cpp inference lib link of windows

As the title

As the title

topk chinese doc code example fails as same input names

* remove FC, test=develop

* delete en_doc for fc, test=develop

* polish code style, test=develop

* change FC to Linear, test=develop

* update load api_cn, test=develop

* polish api comment, test=develop

* fix code bug, test=develop

* polish api comment, test=develop

Add the override function in the elementwise ops

* expose load_program_state and set_program_state api, test=develop

* polist api comment, test=develop

add clear_gradient、current_step_lr api and parameter_list parameter for optimizer in dygraph (#1694)

* add clear_gradient function and parameter_list parameter for optimizer, test=develop

* fix AdagradOptimizer_cn.rst, test=develop

* add sample code, test=develop

* polish sample code, test=develop

* polish description for clear_gradient, test=develop

* add current_step_lr api for optimizer, test=develop

* improve doc of module evaluation and CosineDecay API

* tweak doc of CosineDecay