BAEL-1020 -Introductionjukito (#2634)

* Examples for retrofit guide

* Introduction to Jukito

* class not needed

* Changed to testing module

testing/src/main/java/com/baeldung/introductionjukito/Calculator.java

@@ -0,0 +1,7 @@
+package com.baeldung.introductionjukito;
+
+public interface Calculator {
+
+    public double add(double a, double b);
+
+}

testing/src/main/java/com/baeldung/introductionjukito/ScientificCalculator.java

@@ -0,0 +1,5 @@
+package com.baeldung.introductionjukito;
+
+public class ScientificCalculator extends SimpleCalculator {
+    
+}

testing/src/main/java/com/baeldung/introductionjukito/SimpleCalculator.java

@@ -0,0 +1,10 @@
+package com.baeldung.introductionjukito;
+
+public class SimpleCalculator implements Calculator {
+
+    @Override
+    public double add(double a, double b) {
+        return a+b;
+    }
+
+}