Add extended-monitor

Author: mbax

src/main/java/org/kitteh/irc/client/library/feature/CapabilityManager.java

@@ -105,6 +105,11 @@ final class Defaults {
          */
         public static final String EXTENDED_JOIN = "extended-join";
 
+        /**
+         * Extended monitoring, getting AWAY, ACCOUNT, CHGHOST, AND SETNAME notifications for a MONITOR target.
+         */
+        public static final String EXTENDED_MONITOR = "extended-monitor";
+
         /**
          * Invite notification, not utilized unless requested.
          *