Move Lexer to u16string handling, for unicode support

src/Evaluator/EvalValues/EvalValue.hpp

@@ -31,7 +31,7 @@ public:
     virtual bool EvaluateBool() const{
         throw EvaluationException("Can't evaluate this EvalValue as bool.");
     }
-    virtual const std::string* EvaluateString() const {
+    virtual const std::u16string* EvaluateString() const {
         throw EvaluationException("Can't evaluate this EvalValue as string.");
     }