* add dataset api_cn (#673)

* rm fluid.core in desigin_idea (#674)

* Update fluid_design_idea.md

* Update fluid_design_idea_en.md

* Fix array_read code example error. (#671)
Signed-off-by: Nzhaoyuchen <zhaoyuchen01@baidu.com>

* add data_reader_cn (#676)

* fix doc error (#675)

* update_book_commitid (#680)

* update_book_commitid

* commitid0309

* fix typo

* book indexes (#677)

* thorough clean

* delete_DS_Store

* thorough clean

* delete_DS_Store

* add en index for install doc,fix some expressions

* Appendix title

* add learning_materials_en and update install doc to the latest

* Update learning_materials_en.md