[doc] Make api doc clean #387

The problem

Now google style and numpy style are mixed as doc style.
We need to take one style, so will modify numpy style to google style. (selenium also takes google style)

• google style
  • http://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings
• selenium
  • e.g. https://github.com/SeleniumHQ/selenium/blob/master/py/selenium/webdriver/chrome/options.py

Others

1. https://github.com/appium/python-client/pull/386/files#r285375838