Uses a range of years for Python's copyright rather than listing each year individually.

('2001-2018' vs '2001, 2002, 2003, ...')

Please open an issue on the bug tracker for your change. Since this is related to Python's copyright, it should be approved by BDFL.

I'm sure there are other pull requests and issues that propose this change.

Thanks for your suggestion but, for various reasons, including ease of maintenance across branches, we would prefer to leave the copyright years as they are.

This is a third PR proposing this change. See also #4 and #56.