buttonMarkup: Added deprecation warning.

Author: Gabriel Schulhof

js/jquery.mobile.buttonMarkup.js

@@ -8,6 +8,8 @@
 define( [ "jquery", "./jquery.mobile.core" ], function( jQuery ) {
 //>>excludeEnd("jqmBuildExclude");
 
+// buttonMarkup is deprecated as of 1.4.0 and will be removed in 1.5.0.
+
 (function( $, undefined ) {
 "use strict";