Added doctype for proper embedding

Added doctype to the generated HTML page for ItemDescriptionView. This
corrects a problem where some content like embedded YouTube videos or
podcasts presented in iframes would not render.
Added support for purl.org content tag in rss if present

Purl.org is attempting to create a standard for dealing with dynamic and
changing web content. They have defined an extension to RSS that
provides a more rich rendering of the content in an RSS feed. This tag
is supported by a number of blog engines and, when present, should be
used instead for the description field.
Merge pull request #39 from jbienzms/master

Added doctype for proper embedding