updated citation field example

[Bruce D'Arcus <bruce.darcus@OpenDocument.us>]

FYI, I just changed the citation example to use a new generic field 
(inspired by the earlier citation field):

   <text:structured-field 
meta:class="http://opendocument.xml.org/fields/citation";>
     <text:link
          meta:property="http://purl.org/dc/elements/1.1/source";
          meta:resource="urn:isbn:23980912"/>
     <text:link
          meta:property="http://purl.org/dc/elements/1.1/source";
          meta:resource="urn:isbn:92130926" cite:pages="23"/>
     <text:body>(Doe, 1999: 23; Smith, 2000)</text:body>
   </text:structured-field>

<http://wiki.oasis-open.org/office/Metadata_Examples>

What I've done is moved the referencing logic that I'd earlier had in 
the package to the field itself, since it's important to be able to 
copy-and-paste the content.

Also, I've replaced the meta:href attribute with meta:resource (more 
precise).

Finally, I am assuming here that the cite:pages attribute is understood 
as a parameter of the reference, more than a formal part of the model. 
Am not sure about the implications of this idea generally, but I do 
know in this use case that would be fine.

Still not sure if the meta:class attribute is appropriate, whether it'd 
be better to use meta:property, or invent some new field type 
attribute. (am still learning RDFa, and it''s sometimes tricky figuring 
out exactly how the metadata weaves into the content)

Bruce