* test=develop, test=document_fix

* test=release/1.8, test=document_fix

* this is a test pull-request, test=release/1.8

* fix doc, test=release/1.8

* fix doc, test=release/1.8

* fix doc, test=release/1.8

* add dygraph prepare data doc

* polish based reviewer's comments

* fix details

* update doc of memory optimize

* follow comments, test=develop

* modify the doc, test=develop 

* Update custom_op to support release/1.8
* Make custom_op.md fit release/1.8

update inference library to 1.8.0

cherry-pick PR#2051

* add device_switching doc, test=develop

updata windows_cpp_inference to 1.7.2

* add cluster_quick_start_en.md && fix cluster_quick_start.rst

* translate cluster_quick_start.rst

* update the new version link for the document

delete this document, since this is not related to paddle directly.

* add en doc of memory optimization, test=develop

* follow comments, test=develop

* follow comments, test=develop

update inferecnce lib link to 1.7.1

* add en doc of memory optimization, test=develop

* update new c++ op doc, test=develop

* Revert "add en doc of memory optimization, test=develop"

This reverts commit 17c643e7.

* add disable_dygraph enable_dygraph en cn docs
test=develop

* clean DS_Store
test=develop

* update_fluiddoc_0303,test=develop

* revert_update_advanced_guide,test=develop

* 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 feeding_data.rst, test=develop

* poish description, test=develop

* fix data shape, test=develop

* 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

* update cpu distribute practice