Replace deprecated distutils.version

Since python 3.8, using distutils Version is deprecated.

Use fix proposed by @proto3:

• Use "packaging" module instead, as recommended in the warning.
• Remove the "requires" keyword in setup.py, which is deprecated too (https://setuptools.pypa.io/en/latest/userguide/declarative_config.html#metadata), to only use install_requires.

Closes #489 (closed)