Content of Subject element should be xrd:anyURI

According to the xrd-1.0 schema, the content of the Subject element should be xrd:anyURI (a simple extension of xs:anyURI). Rather than repeat the metadata location in the Subject element, the latter is now set to the InCommon registrar ID.
Merge pull request #51 from trscavo/patch-3

Content of Subject element should be xrd:anyURI