Add a new field in the AttributeExchange to support Yahoo display names.

Yahoo does not return "http://axschema.org/namePerson/first", but requires
"http://axschema.org/namePerson" instead.  This commit adds the attribute.
Merge pull request #10 from jplyle/Add-Attribute-Exchange-namePerson-Field

Add a new field in the AttributeExchange to support Yahoo display names.