Also update the Metadata-Version when adding Requires-Python

Add missing blank lines after class or function definition.

Add python_requires keywords to setup

Put colon-separated compound statement on separate lines.

Format block comment.

Test for membership should be 'not in'.

Put imports in same block alphabeticaly.

Make exactly one space after comma.

Match closing bracket identation of opening bracket's line.

Fix spacing after comment hash.

Remove whitespace around parameter '=' sign.

Fix missing whitespace around operator.

Use isinstance() instead of type() for a typecheck.

This should allow setuptools to write the metadata Requires-Python and
Requires-External from PEP345 to the PKGINFO file