created Hello World generator per issue #195 (#270)

Author: morrme

generators/Exercises/HelloWorldExercise.cs

@@ -0,0 +1,9 @@
+namespace Generators.Exercises
+{
+    public class HelloWorldExercise : EqualityExercise
+    {
+        public HelloWorldExercise() : base("hello-world")
+        {
+        }
+    }
+}