IHE - Document Sharing

As indicated XDS-I provides the link to the Imaging world from a Document Sharing exchange. The Document Sharing exchange is not sufficiently described in the section. I recommend that Document Sharing exchange be more comprehensively expressed thru use of the IHE Whitepaper on Health Information Exchange. Thus removing mentions of PIX and PDQ as these are just a fragment of needed infrastructure that also includes Security, Privacy, Discovery, Retrieve, and management.