Fixed some Expression and Operand memory issues.

Operand.h

@@ -1,7 +1,7 @@
 #ifndef __Operand_h__
 #define __Operand_h__
 
-#include "ZString.h"
+#include "MString.h"
 
 namespace jet {
 
@@ -19,7 +19,7 @@ namespace jet {
       ///
       
       bool boolean;
-      coreutils::ZString string;
+      coreutils::MString string;
       
     private:
 //      dataType enum ={};