* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* enhance the op_version_registry, test=develop

* add unittests, test=develop

* enhance the op_version_registry, test=develop

* fix bugs, test=develop

* revert pybind_boost_headers.h, test=develop

* fix a attribute bug, test=develop