* add missing get_program_persistable_vars and get_program_parameter doc
test=develop

* add missing save doc, add link
test=develop

* update load api_cn, test=develop

* polish api comment, test=develop

* fix code bug, test=develop

* polish api comment, test=develop

* expose load_program_state and set_program_state api, test=develop

* polist api comment, test=develop

* fix chain doc, test=develop, test=document_preview

* refine some reader API

* import paddle.fluid, test=develop

* follow comment, test=develop

test=document_fix

* add save load save_dygraph load_dygraph, test=develop

* add .idea in gitignore, test=develop

* minor fix, test=develop

* doc refines, test=develop

* doc refines, test=develop

* fix the doc format of io.chain.

* fix io_batch develop=test

* fix io_batch develop=test

* rewrite batch_cn.rst test=develop

* rewrite batch_cn.rst test=develop

* fix PyReader develop=test

* rewrite PyReader_cn.rst develop=test

* fix save_persistables  develop=test

* fix save_persistables develop=test

* rewrite save_persistables_cn.rst test=develop

* refine save_params develop=test

* fix save_params develop=test

* Rewrite save_params_cn.rst develop=test

* fix save_params develop=test

* rewrite save_params_cn.rst test=develop

* remove map_readers from reader API

* modify io_map_readers

* modify io.compose inference doc

* Rewrite the content of load_persistables_cn.rst.

* refine api comments

* refine api comments

* update docs

* update docs

* Rewrite the content of the chain in Reader_cn.rst.

* Rewrite the content of load_params_cn.rst.

* use default_main_program instead of _main_program_.

* update save_vars and load_vars, test=develop

* Rewrite firstn and shuffle functions, test=develop

* fix doc for PipyReader test=develop

* fix doc for PipyReader test=develop

* fix according reviewer advice test=develop

* add data loader doc, test=develop

* follow comments, test=develop

* follow comments again, test=develop

* rewrite the content of load_inference_model_cn.rst.

* fixed one error of http://newicafe.baidu.com/issue/DLTP-2186/show

* update api_cn of develop

* fixed some errors of http://newicafe.baidu.com/issue/DLTP-2129/show

* modify fluid.rst and layers.rst and gen_doc.py

* synchronize api_cn of develop 0823,test=document_preview

* update io_cn.rst

* delete ComposeNotAligned_cn.rst

* http://newicafe.baidu.com/issue/DLTP-2069/show?from=page

* fixed one error of develop

* fixed one error of api_cn

* fixed some errors of api_cn

* fixed some errors of api_cn

* fixed two errors.

* fixed two errors

* fixed one error.

* fixed one error

* fixed one error.

* fixed two errors.

* fixed one error.

* fixed two errors

* fixed two links

* synchronize api_cn with the api_en of develop.

* updated develop/api_cn

* update the api_cn of develop

* update api_cn of develop

* fixed some errors

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* Delete .DS_Store

* fixed some wrong links

* fixed two links

* fixed two links and some error.

* fixed some errors.

* fixed two links