Rework evaluation to use shared pointers, fix bugs

src/Evaluator/EvalValues/StringEvalValue.hpp

@@ -29,8 +29,8 @@ public:
         return _value;
     }
 
-    EvalValue* Clone() final{
-        return new StringEvalValue(_value);
+    shared_ptr<EvalValue> Clone() final{
+        return make_shared<StringEvalValue>(_value);
     }
 };