Add ability to document IRIs

This patch introduces the ability to document IRIs generated from an
RDFS or OWL vocabulary.  It does not provide any documentation for
such IRIs, though, so there should be no change in the generated
documentation after applying this patch.

src/Data/RDF/Vocabulary/Generator/VocabularyGenerator.hs

@@ -64,7 +64,7 @@ vocabulary graph =
         subject <- nub $ subjectOf <$> triplesOf graph
         iri <- maybeToList $ toIRI subject
         name <- maybeToList $ iriToName iri
-        return (name, declareIRI name iri)
+        return (name, declareIRI name iri Nothing)
       (PrefixMappings prefixMappings') = prefixMappings graph
       namespaceDecls = do
         (prefix, iri) <- M.toList prefixMappings'
@@ -87,11 +87,13 @@ unodeFun = VarE $ mkName "Data.RDF.Types.unode"
 mkPrefixedNSFun :: Exp
 mkPrefixedNSFun = VarE $ mkName "Data.RDF.Namespace.mkPrefixedNS"
 
-declareIRI :: Name -> Text -> Q Dec
-declareIRI name iri =
+declareIRI :: Name -> Text -> Maybe Text -> Q Dec
+declareIRI name iri comment =
   let iriLiteral = LitE . StringL $ T.unpack iri
       unodeLiteral = AppE unodeFun $ AppE packFun iriLiteral
-   in funD name [return $ Clause [] (NormalB unodeLiteral) []]
+   in funD_doc name [return $ Clause [] (NormalB unodeLiteral) []]
+               (T.unpack <$> comment)
+               [Nothing]
 
 declareIRIs :: [Name] -> Q Dec
 declareIRIs names =