* 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

* add dist erfinv gumbel softmax

* fix test gumbel softmax op bug

* try to fix gumbel softmax error

* add label smooth backlist

* add erfinv API, test=develop

* fix gradient accuracy error, test=develop

* fix cuda compilation error on Windows, test=develop

* fix M_2_SQRTPI undeclared identifier on Windows, test=develop