Added asDouble method to ZString.

ZString.cpp

@@ -1,6 +1,7 @@
 #include "ZString.h"
 #include "Log.h"
 #include "Exception.h"
+#include <stdlib.h>
 #include <iostream>
 
 namespace coreutils {
@@ -106,6 +107,10 @@ namespace coreutils {
       return tempInt;
    }
 
+   double ZString::asDouble() {
+      return strtod(cursor, &cursor);
+   }
+
    int ZString::incrementCursor(int length) {
       char *temp = cursor;
       if((cursor + length) > (data + this->length))