* add code and docs for ppclas examples
* fix doc
* add code for printing results
* add ppcls demo and docs
* modify example according to refined c api
* modify example code and docs for ppcls and ppdet
* modify example code and docs for ppcls and ppdet
* update ppdet demo
* fix demo codes
* fix doc
* release resource when failed
* fix
* fix name
* fix name