Added VPAT (PDF) and other accessibility fixes.

The link to the VPAT is itself accessible. All pages with PDF files now have an (accessibly hidden) paragraph linking to the Adobe Reader app.  The VPAT notes that some archival media from the 2013 Membership Meeting has not been transcribed, nor do we have links to all required viewers.
Unrelated typo in title of Membership Meeting 2013 page.
Replacing &reg; entity with numeric equivalent.
Fix xhtml syntax in repository.xhtml
Update Last Revised date in repository.xhtml