Add xref config.

Author: gkellogg

index.html

@@ -36,6 +36,9 @@
       doJsonLd:               true,
       pluralize:              true,
 
+      // Cross-reference definitions
+      xref: ["json-ld11", "json-ld11-api", "json-ld11-framing"],
+
       // if you want to have extra CSS, append them to this list
       // it is recommended that the respec.css stylesheet be kept
       // extraCSS:             [],