Added support for calling script functions

PorygonSharpTests/UnitTest1.cs

@@ -93,5 +93,19 @@ namespace PorygonSharpTests
             }
         }
 
+        [Test]
+        public void Test8()
+        {
+            using (var script = new Script("function add(number a, number b) result = a + b end"))
+            {
+                script.Evaluate();
+                script.CallFunction("add", 100, 50);
+                var variable = script.GetVariable("result");
+                Assert.AreEqual(TypeClass.Number, variable.GetTypeClass());
+                var val = variable.EvaluateInteger();
+                Assert.AreEqual(150, val);
+            }
+        }
+
     }
 }