Fix stripping of HTML tags in ATOM feed content

Preparse ATOM feeds in an attempt to standardize cdata, escaped, and raw html content.  If the content is not already wrapped in CDATA, it will now unescape the html and wrap the content in CDATA so that Nokogiri won't parse and strip out the tags.

All tests are green under 1.9.2 but only when using my patched version of the sax-machine fork by ezkl.

Mine: https://github.com/davekrupinski/sax-machine (Pending Pull Request with EZKL fork)
Fork: https://github.com/ezkl/sax-machine

Have added notes for future improvements, but does satisfy my base requirements of properly handling atom feeds with differing content nodes.

Dave