* Add profiling information for inference example, recognize digits.

* Refine the profiling method.

* Correct the use of RecordEvent and simplify recognize_digits.

* fix absolute include path

* Remove test_helper.h in old location

* update include path

* Save the inference model in Python example of recommender_system.

* Add infer() in Python unittest recommender_system.

* Add C++ inference unittest of recommender_system.

* First basic implementation

* Add infer example for image_classification

* Address review comments: round 1

Enable whole-archive flag in cc_test and use cc_test to rewrite the CMakeLists.txt of inference unittest.