* 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.

* add dygraph parallel env doc, test=develop

* polish details, test=develop, test=document_fix

* fix examples error in other apis, test=develop

* fix more example error in other api, test=develop

* add white list for gpu examples, test=develop, test=document_fix