Update to 1.57
    
    - New upstream release 1.57
      - The last release would die if Sub::Util was not available, but this
        should just be an optional requirement (GH#131); this is the second
        time I've introduced this bug, so now there's a test to make sure
        that DateTime can be loaded if Sub::Util is not installed, which will
        hopefully prevent a third occurrence of this bug