* 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 filter_by_instag out_val_ifempty cn api test=develop

* change out_val_ifempty to out_val_if_empty in filter_by_instag test=develop

fix python3 installation problem on Windows

In elementwise_min api doc has the error, all the api just use the elementwise_max op, we just correct the doc.

* 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

* add missing get_program_persistable_vars and get_program_parameter doc
test=develop

* add missing save doc, add link
test=develop

* add tracer_option in function about profiler test=develop

* fix the conda install doc test=develop

Fix the pow doc bug, change the pow parameter from 2.0 to 3.0

Fix the compare op force_cpu params  bug

* update_fluiddoc_0228,test=develop

* Update release_note_cn.md
Co-authored-by: NDaniel Yang <grasswolfs@163.com>

* add conda english doc test=develop

* add conda install english doc test=develop

This reverts commit 230b6915.

* 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

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

* remove dead link

* 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.

remove redundant index item

upgrade api for rec_case

* 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