Implementato Iterator in NodePositionList e aggiunto solo i prototipi nelle altre classe che implementano Sequence

position/PositionList.java

@@ -9,7 +9,7 @@ import  exceptions.*;
 //Copyright (c) 2003 Brown University, Providence, RI
 //Additional modifications and methods by xgiovio
 
-public interface PositionList<E> {
+public interface PositionList<E> extends Iterable<E> {
 
 
   public int size();