* Support python3.8

test=notest

* Fix install pr requirements.txt

* test=document_fix

* Add details to the summary and test it, test=document_fix

* Add set +e before example, test=document_fix

* Remove test code, test=document_fix

* Optimize summary information and test it, test=document_fix

* Remove test code, test=document_fix

* Restore file changes caused by pre-commit and test it, test=document_fix

* Change argument of checkout, test=document_fix

* Remove test code, test=document_fix

* add retry on mac

* fix some error

* fix with some errors

* Show more possible problems with build_and_check in file paddle_build.sh, test=develop

* Remove test codes modified in file device.py for build_and_check, test=document_fix

* Fix missing blank space in file device.py, test=document_fix

* Final process via summary_check_problems function, test=document_fix

* Add the option to execute unit tests only at night

* set ut nightly label for 3 cases.

* add unittest for paddlerolemaker with gloo

* Fix inference bug

* fix inference lib

* add fleetrun command for distributed running; test=develop

* add ci check for changing op-related api without core.ops, test=develop

* generate api_source_md5 file when build, test=develop

* add failed example, test=develop

* add failed example, test=develop

* handle exception, test=develop

* add reinforcement learning model test=develop

* align backward test=develop

* add gym in paddle_build.sh test=develop

* rm pip install in script test=develop

* refine paddle_build.sh test=develop

* fix sed error in macOS test=develop

* polish code test=develop

* Merge hapi into Paddle

Hapi is a high level API for training and inference.
The main modules include Model, Loss, Metrics, Dataset.
Also includes common modules and models in NLP and computer vision, such as BERT, ResNet.

These modules are developed by:
0YuanZhang0, guoshengCS heavengate, LielinJiang, qingqing01, xyzhou-puck huangjun12, wangxiao1021, zhangyang.

test=develop