Update to 2.21
    
    - New upstream release 2.21
      - Patch Makefile.PL to refer to the current repo, which is on github, and
        not the original one, which is on Adam's web site (CPAN RT#102125)
      - Remove Build.PL (CPAN RT#102126)
      - Edit line lengths in the Changes file to a maximum of 100 characters
      - Edit line lengths in the docs the same way
      - Expand the SEE ALSO section of the docs
    - Use %license