* add unused input vars check for OpWithKernel, test=develop

* remove unused vars in some ops, test=develop

* fix batch_norm, test=develop

* add white list, test=develop

* add CI check for white list, test=develop

* :ove white list to c++, test=develop

* solve failure of CI, test=develop

* add unittest for unused_var_check, test=develop

* refine code, enable check in operator_test, test=develop

* skip mkldnn, test=develop

* extend white list, test=develop

* refine condition of mkldnn, test=develop

* fix paddle_build, test=develop

* follow comments, test=develop

* fix GetExpectedKernelType

* add wiki ref to err_msg, test=develop

* follow comment, test=develop

* optimization check_api_approvals

* change echo line

* echo_line

* update

* test=develop;test=document_fix

* change api document review;test=develop;test=document_fix

* test=develop;test=document_fix

* fix PADDLE_ENFORCE ci check bug, test=develop, test=document_fix

* fix PADDLE_ENFORCE match error, test=develop, test=document_fix

* add ci check for error message specification, test=develop, test=document_fix

* replace spec url & refine failed message, test=develop, test=document_fix

* split api_spec document;test=document_fix

* change tools

* test=develop;test=document_fix

* test=develop;test=document_fix

* add op indicate var type method call check

* add error test example, test=develop, test=document_fix

* add count judge, test=develop, test=document_fix

* polish example detail, test=develop, test=document_fix

* test indicate var data type method, test=develop, test=document_fix

* test no get expect kernel type, test=develop, test=document_fix

* remove test case, test=develop test=document_fix

* refine API.spec, test=develop

* add nn.py to test,test=develop

* fix by removing new.spec, test=develop, test=document_fix

* refine scripts when PYTHON_ABI is empty, follow partial comments, add extra cpp api doc, test=develop, test=document_fix

* remove extra doc changes, remove API.spec, test=develop