* add paddle new save load doc

* move static save apis & polish multiple details

* add api mapping

* move apis place

* fix example code error

* polish model save load guide

* polish example code

* fix details example error

* polish guide doc

* change title format

* remove history reason

* remove other history reason

* add enable_static for old save/load

* add enable_static for old api

test=develop

* Add example for buffered and cache, test=develop, test=document_fix

* up, test=develop;test=document_fix

* test=document, bug fix

* test=develop, add utilbase doc

* test=develop, bug fix

* test=develop, ci

* test=develop, ci

* test=develop, rm fs

* remove paddle.reader APIs. test=develop

* remove paddle.reader

* link fix

* add dygraph cn_doc;test=develop

* update doc

* add fleet meta lars and lamb api document

* add fleet meta lars and lamb api document

* test=develop

* update doc for hapi.model.save and hapi.model.Model in 2.0-RC

* fix example code for Model

* fix doc for Model example code

* fix sample code, add import InputSpec

* add fleet cn_doc;test=develop

Co-authored-by: Nroot <root@yq01-qianmo-com-255-129-13.yq01.baidu.com>

* add docs

* add Tensor concept introduction

* add Tensor concept introduction

* add Tensor concept introduction

* add Tensor concept introduction

* add Tensor concept introduction

* fix example code

* Update paddle/metrics

* Fix format

* Update Metric format

* update hapi Model doc

* add summary

* mv Model_cn.rst to model dir

* fix hapi test=develop

* fix_model test=develop

* fix gen_doc test=develop

* fix alias_mapping

* fix_gen_doc test=develop

* fix hapi test=develop

* fix model test=develop

* add formula for entropy and kl-divergence

* fix formula in cn doc

* fix formula for Normal

* add paddle.io. test=develop

* fix indent. test=develop

* remove alias test=develop

* remove api_attr

* add_apis_and_fix_alias

* fix code bugs

* fix___init_bug

* fix migration guide

* add api_reference test=develop

* fix style test=develop

* change faq to chinese test=develop

* add release note en

* fix release note test=develop

* fix api_reference test=develop

* fix style test=develop

* add paddle.vision.transforms.* api cn doc

* add alias for paddle.vision.transforms

* delete invalid file

* add some empty doc file for rd

* delete some text alias

* change some doc path

* add some hapi cn docs