* [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

* move momentum, rmsprop to phi; test=develop

* update

* update

* update

* update

* udpate; test=develop

* fix xpu npu bugs; test=develop

* fix npu bug; test=develop

* fix windows compile error; test=develop

* fix windows compile error; test=develop

* polish code; test=develop

* fix conflict; test=develop

* add meshgrid;

* update

* polish code

* polish code;

* fix bug

* format; remove useless code

* fix npu bug

* fix bug

According to paddle 2.0 standard.
1, chang api to def meshgrid(*args, **kwargs) we hide name argument in **kwargs.
2, add relate ut.
3, change example code to imperative mode

* test=develop fix api doc error