Use install command from distutils (fix regression)

Use the install command from *distutils* since the install command from
*setuptools*:

- does not invoke the build commands properly
- puts data files in the egg directory rather than in the system
  directory

The bug was introduced by subclassing only install_data rather than
install (dd0c634). Although, the install command from setuptools was
subclassed before, the actual installation logic would still be from
distutils. This is due to some really odd call-context checks in the
setuptools command.
Update README to fixed setup.py install command