Update to 1.20
    
    - New upstream release 1.20
      - Use "say" in synopsis
      - Remove needless special characters in doc section
      - Change doc =item attributes for new to =head for index
      - Add known_attributes function/method
      - Add contributor notes
      - Allow undef as value for aliased attributes
    - Explicitly BR: perl-devel, needed for EXTERN.h