Add cross-attention cache for dygraph Transformer.
Add greedy search for dygraph Transformer.

* add yolov3 for dygraph

* add readme.md for ptb_lm, test=develop

* fix ptb_dy.py to eval valid_data, test=develop

* fix ptb_dy.py to eval valid_data, test=develop

* add the fp16 support for ResNet50

* add docs for AMP.

* lac dygraph for version 1.7

* lac dygraph for version 1.7

* add eval, predict and README

* remove unused links

* fix lac_dygraph download and README

* lac dygraph for version 1.7

* lac dygraph for version 1.7

* add eval, predict and README

* remove unused links

* adapte senta

* upgrade senta

* modify gru network

* fix bugs in gru and bigru net

* fix channels in cnn net

* add pwcnet

* add SemSegPaddle

* update README.md

* add rrpn for models

* upload dygraph seq2seq for v1.6.2

* update README

* upgrade to version 1.7

* remove unused line

remove unused line

* fix base_output dirname

* update run.sh to be the same as static graph

* update run.sh to be the same as static graph

* update Readme

* update Readme

* update README.md

change version number to 1.7

* update transformer support remove build once; test=develop

* fix optimizer; test=develop

* add new model, bmn dygraph model for video temporal proposal generation

* matching new API, decoupling model and  train module

* fix train reader usage error

* fix cpu num set error

* fixed eval/test func

* change pred/eval to 1 thread or 1 gpu card
Co-authored-by: NChen Weihang <sunny_cwh@163.com>