* Enhance dataloader robustness

* Fix the bug about unexpected exiting when reading image failed

* Adapt to PaddleHub2.0 to eliminate warning
* Fix the training log format

* fix predict

* fix export model

* fix doc

* Fix the timing of hubserving

* add enable benchmark for lite

* fix config

* Fix "tar" to "pdparams" to adapt to dygraph

* Update the download link of Paddle Inference Library

* fix trt doc

* update history

* fix cpp time

* fix time

Fix some description of documentations

* Modify the "cls_model_dir" to "cls_model_path" and "cls_params_path"

add mkldnn config

add hub serving code and doc

fix python and cpp inference

1. fix dist training 
2. fix cpp infer to support dir inference