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

composite/src/main/java/com/iluwatar/composite/LetterComposite.java

@@ -24,6 +24,9 @@ public abstract class LetterComposite {
 
   protected abstract void printThisAfter();
 
+  /**
+   * Print
+   */
   public void print() {
     printThisBefore();
     for (LetterComposite letter : children) {

composite/src/main/java/com/iluwatar/composite/Sentence.java

@@ -9,6 +9,9 @@ import java.util.List;
  */
 public class Sentence extends LetterComposite {
 
+  /**
+   * Constructor
+   */
   public Sentence(List<Word> words) {
     for (Word w : words) {
       this.add(w);

composite/src/main/java/com/iluwatar/composite/Word.java

@@ -9,6 +9,9 @@ import java.util.List;
  */
 public class Word extends LetterComposite {
 
+  /**
+   * Constructor
+   */
   public Word(List<Letter> letters) {
     for (Letter l : letters) {
       this.add(l);