• Digest::SHA now a subclass of Digest::base
  -- inherits hexdigest/b64digest/addfile methods
  
• added "hashsize" method
  
• removed old "shaopen()/shawrite()/..." legacy code
  -- in favor of standard, streamlined OO interface
  
• renamed test vector files from NIST
  -- prevents problems on 8+3 filesystems
  
• added test for Dave Ireland's SHA-256 vector