Added exercise 3

Exercise3/Exercise3.java

+package fi.utu.tech.ooj.exercise4.exercise3;
+
+interface Winged {
+    default void fly() {
+        System.out.println(this + " flies!");
+    }
+}
+
+interface Bipedal {
+    default void walk() {
+        System.out.println(this + " walks!");
+    }
+}
+
+abstract class Bird implements Winged, Bipedal {
+
+}
+
+class Crow extends Bird {
+    private static int idx = 0;
+    private int id = ++idx;
+
+    @Override
+    public String toString() {
+        return "Varis " + id;
+    }
+}
+
+public class Teht3 {
+    public Teht3() {
+        System.out.println("Exercise 3");
+
+        challenge1(new Crow());
+        challenge2(new Crow());
+    }
+
+    void challenge1(Bird b) {
+        System.out.println("In this challenge, we fly and then we walk!");
+
+        b.fly();
+        b.walk();
+    }
+
+    <X extends Winged & Bipedal> void challenge2(X b) {
+        System.out.println("In this challenge, we fly and then we walk!");
+
+        b.fly();
+        b.walk();
+    }
+}