Adjust checkstyle rules. Make checkstyle fail the build when violations are found. Correct all current checkstyle violations.

specification/src/main/java/com/iluwatar/specification/app/App.java

@@ -31,6 +31,9 @@ import com.iluwatar.specification.selector.MovementSelector;
  */
 public class App {
 
+  /**
+   * Program entry point
+   */
   public static void main(String[] args) {
     // initialize creatures list
     List<Creature> creatures =

specification/src/main/java/com/iluwatar/specification/creature/AbstractCreature.java

@@ -16,6 +16,9 @@ public abstract class AbstractCreature implements Creature {
   private Movement movement;
   private Color color;
 
+  /**
+   * Constructor
+   */
   public AbstractCreature(String name, Size size, Movement movement, Color color) {
     this.name = name;
     this.size = size;