Removing the LTSW source.

- This list has not been updated since 2002, and the use of the
  reference link in the source has been inconsistent at best.
Rewriting IANA registry parsing.

- The IANA registry format changed layout in (X)HTML, but an XML version
  was made available that is far easier to parse and provides more
  useful information.
- Adding #xrefs/#xrefs_urls to MIME::Type to reflect the more useful
  data available in the new IANA registry XML format. Over time,
  #references and #urls will be views on the #xrefs data.
Removing an unused Rakefile task.
Summarizing the impending mime-types 2.1 release.