* add register_forward_hook api for Layer, test=develop

* fix sample code, test=develop

fix Chinese doc bug in argsort, add the dtype support of dtypes

fix sample code diff for OP(retinanet_detection_output, retinanet_target_assign), fix `gamma` default value for OP(sigmoid_focal_loss) (#1971)

* fix sample code diff for OP(retinanet_detection_output, retinanet_target_assign), fix  default value for OP(sigmoid_focal_loss). test=develop

* fix float value. test=develop

add the compatibility statement in release notes

* add api_cn

* test=develop

* add paddle.tensor

* add

* fix program api sample code error

* fix detail error

* fix build strategy cn doc sample code diff

* fix code error

* fix execution strategy error

* fix LayerNorm error

fix regularizaiton documention to dispel puzzle of user

Refine the doc of create_global_var, pad, pad_constant_like and pad2d to make it consistent with en doc.

* sync recompute doc btw zh and en, test=document_preview

* test=preview

* add inplace_abn. test=develop

* change gen_doc

* change gen_doc

* add cluster_quick_start_en.md && fix cluster_quick_start.rst

* translate cluster_quick_start.rst

* update the new version link for the document

* fix lstm doc error

* fix lstm doc error

* remove unused line in lstm doc

* Add learning_rate in NoamDecay test=develop

* Update sample code test=develop

* add DataLoader drop_last doc, test=develop

* follow comments, test=develop, test=document_fix

delete this document, since this is not related to paddle directly.

* add update for gelu: approximation option

* update english installation documents, test=develop

* fix index_en.rst, test=develop