The template for a port Makefile can be used automatically by editors
like vim. It hasn't been updated since its introduction in 2014 though.
Modernize and extend it to meet current best practices:
- Replace PORTVERSION with DISTVERSION, which is now the preferred variable to use.
- Add the WWW variable which should be set for every port.
- Add the LICENSE and LICENSE_FILE variables which should also be set whenever possible.