prefer `pip install`

[wyli]

Is your feature request related to a problem? Please describe.
the python setup.py based installation approaches are discouraged

running develop
/usr/local/python3.7/site-packages/setuptools/command/easy_install.py:159: EasyInstallDeprecationWarning: easy_install command is deprecated. Use build and pip and other standards-based tools.
  EasyInstallDeprecationWarning,
/usr/local/python3.7/site-packages/setuptools/command/install.py:37: SetuptoolsDeprecationWarning: setup.py install is deprecated. Use build and pip and other standards-based tools.
  setuptools.SetuptoolsDeprecationWarning,

documentation and test scripts should be updated to use pip install

• see also a similar approach used by cupy https://github.com/cupy/cupy/pull/985/files