1. use set_value() to set weight.
2. use weight in PositionEmbedding instead of protected member `_w`.
3. fix data layout for Embedding, the tailing sized-1 dimension is removed, update documentation, 
4. fix tensorboard tags, spaces are replaced with `_`.

* fix paddlerec dnn loss nan

* change hash with mmh3.hash in dnn

* fix get cuda device bug when only use cpu

* fix typo

* fix step time in vae

* fix step time in vae

* refix point_rcnn elementwise compatible.

* remove axis=0 in get_reg_loss

* fix point_rcnn elementwise_compatable

* Update GETTING_STARTED_cn.md

* Update x2coco.py

* create

* Update README.md

This reverts commit ab0920d3.

test=develop

test=develop

* add PointRCNN model
   by heavengate, FDInSky, tink2123

* update ptb model to use auto generated op functions, test=develop

* refine model code, test=develop

* refine model code, test=develop

* refine warning

* add post training quantization demo, test=develop

* update, test=develop

* fix python3 compatable.

* update weight download link

* cherry-pick 1.6 to develop

* fix outdated layers.nn api

* fix outdated layers.nn api

* fix open utf8

* Add hrnet,res2net and some resnext pretrained models