Add Extensions to biblio.

--HG--
extra : rebase_source : c3ed632fe02fe1a42aad66f3b0eb637764b0a324

Author: tabatkins

biblio.ref

@@ -632,6 +632,13 @@
 %D 15 September 2011
 %U http://www.w3.org/TR/2011/WD-css-device-adapt-20110915/
 
+%L CSS-EXTENSIONS
+%T CSS Extensions
+%A Tab Atkins Jr.
+%S W3C Editor's Draft
+%O (Work in progress.)
+%U http://dev.w3.org/csswg/css-extensions/
+
 %L CSS-MASKING
 %T CSS Masking Level 1
 %A Dirk Schulze