Log Message:
Update to 1.13

Upstream changes:
1.13
        30 Oct 2018
        - Add function pl_translate(), by request.
        - Turn README into README.md. With MetaCPAN replacing CPAN,
          there is no reason to have a plain-text README anymore
          (MetaCPAN doesn't treat the file as special).
        - Add a CONTRIBUTING.md file, which is becoming a thing.
        - New test file for pl_translate(), and upgrade test files
          that for some reason were still using Test::Simple to Test::More.
        - Added an :all tag. Why not.