Merge pull request #2 from flh/rdf_dc

Add Dublin Core IRIs.
add all dc elements and terms with comments
add headers + fix deprecated or operator
move to future 0.11 version of stog
add missing files after moving to stog 0.11
Only output one <rdf:Description> for each node

The following RDF/XML part:

  <rdf:Description rdf:about="http://zoggy.github.io/ocaml-rdf/">
    <dc:title>OCaml-RDF</dc:title>
  </rdf:Description>
  <rdf:Description rdf:about="http://zoggy.github.io/ocaml-rdf/">
    <dc:description>
      OCaml-RDF is an OCaml library to manipulate RDF
      graphs and execute Sparql queries.
    </dc:description>
  </rdf:Description>

describes exactly the same graph as:

  <rdf:Description rdf:about="http://zoggy.github.io/ocaml-rdf/">
    <dc:title>OCaml-RDF</dc:title>
    <dc:description>
      OCaml-RDF is an OCaml library to manipulate RDF
      graphs and execute Sparql queries.
    </dc:description>
  </rdf:Description>

The latter is less verbose, more idiomatic and more human-readable. This
patch changes Rdf_xml.output so that only one <rdf:Description> is
created for each subject node in the graph.