* static model runner basic implement, test=develop

* add run program op to execute loaded program, test=develop

* refactor static model runner & run program op, test=develop

* reset engine.cc to resolve conflict

* adapt the change of dygraph double grad, test=develop

* refactor impl to solve control flow error, test=develop

* clear debug code, test=develop

* fix ci str compatible error & checkout dygraph grad maker & add example, test=develop

* hide api & add op test, test=develop

* fix run program op test places error, test=develop

* fix program by review comment, test=develop

* delete change var desc name, test=develop

* fix other program by review comment, test=develop

* remove _static_graph_guard, test=develop

* add selectedrows test, test=develop

* remove desc parser, test=develop

* fix detail program, test=develop

* change socpe create & add test, test=develop

* expose dygraph.grad api, test=develop, test=document_fix

* add more parameter in dygraph.grad API, test=develop

* add only_inputs=True parameter, test=develop

* follow comments, test=develop, test=document_fix

* fix typo, test=develop, test=document_fix

* add double grad implementation for dygraph, test=develop

* polish code, add uts, test=develop

* fix place bug, test=develop

* polish codes, add more uts for coverages, test=develop

* add no_grad_set, test=develop

* add star gan ut, test=develop

* follow comments, test=develop