Adds string conversion for xml output of semantic tree. Fixes issue #248.

Author: zorkow

lib/mj-single.js

@@ -549,9 +549,8 @@ function GetSpeech(result) {
 function GetSemantic(result) {
   if (!data.semantic) return;
   result.streeJson = speech.toJson(result.mml);
-  result.streeXml = data.minSTree ?
-    speech.toSemantic(result.mml) :
-    speech.pprintXML(speech.toSemantic(result.mml));
+  var xml = speech.toSemantic(result.mml).toString();
+  result.streeXml = data.minSTree ? xml : speech.pprintXML(xml);
 }
 
 //