* upgrade guide added

* update migration tool page

* minor change

* minor change

* update codes and format

* no ci for upgrade_guide

* minor

* minor

* 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

* polish data read faq

* polish details

* remove static mode fag

* add fleet cn_doc;test=develop

We think we should split the usage and architecture because of clear organization and future extension (we may add more usage guide)

* fix windows pip install

* change =

* change =

* fix die link

* fix

* migrate en doc from old dir

* fix typo

* fix typo

* fix typo

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 en release note test=develop

* fix release note test=develop

* 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

* fix tutorial test=develop

* fix pic test=develop

* update tutorial test=develop

* remove alias test=develop

* remove api_attr

* add_apis_and_fix_alias

* fix code bugs