implemented variables and function call evaluation

src/main/java/de/hsrm/compiler/Klang/nodes/expressions/Variable.java

@@ -0,0 +1,18 @@
+package de.hsrm.compiler.Klang.nodes.expressions;
+
+import de.hsrm.compiler.Klang.visitors.Visitor;
+
+public class Variable extends Expression {
+
+    public String name;
+
+    public Variable(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public <R> R welcome(Visitor<R> v) {
+        return v.visit(this);
+    }
+
+}