Add a converter for the Europeana Data Model

[johnjung]

Add a MarcXmlToEDM() class to classes.py.

The Europeana website has documentation about the Europeana Data Model (EDM) in general.
These notes are about how our MARC records should be converted to EDM triples. As you work, if you have questions about this document, we can talk to David Bietila for clarification.

You should output the triples in the Turtle syntax.