* rm dropout

* fix_dead links and remove dropout

[cherry-pick 2.0-beta][Dy2Stat] Fix doc of error_handling and debugging according to reviews (#2620) (#2638)

* migrate en doc from old dir

* fix typo

* fix typo

* fix typo

* 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

cherry pick 2544, add formula for entropy and kl-divergence in Uniform and Normal classes (#2544) (#2616)

* add formula for entropy and kl-divergence

* fix formula in cn doc

* fix formula for Normal

* fix_hapi_path for 2.0-beta

* fix alias

* 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

* 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 input_spec cn

* add input_spec cn

* fix === style

* fix file name typo

* add ref

* add en doc

* fix en doc

* refine according reviewer

* remove user comment

* refine doc

* refine doc

* 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

* Add English doc of debugging

* Add English doc of error_handling

* add release note

* fix_style

* fix_style

* remove @name 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