figure out best way to associate contributors with documents

[baskaufs]

Currently, all known contributors to standards documents have been linked via dcterms:contributor as required by the Standards Documentation Specification. However, this generic link doesn't capture the variety of roles, such as author, editor, first author, translator, etc. I've generated links using properties from the gndo: (http://d-nb.info/standards/elementset/gnd#) vocabulary as a separate dataset, but haven't figured out an elegant way to include those connections directly in the document metadata itself. Guid-O-Matic currently can't handle extension tables that are linked to the core table by varying properties.