Bug 6594: Schema.org structured data for OPAC display

Bug 6594: Schema.org structured data for OPAC display

To support schema.org processors, such as Google, Bing, and Yandex,
structure our data so that it has machine-readable attributes. This pass
declares the CreativeWork sub-types as well as Product for the main
bibliographic record details, and uses the Offer type for holdings
information per the W3C Schema Bib Extend community group discussions.

Signed-off-by: Dan Scott <dan@coffeecode.net>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Comments on final patch.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>