implementato nodeposition con to string e reverse. aggiunto copyright

position/Position.java

@@ -0,0 +1,14 @@
+package position;
+/**
+ * An interface for a position, which is a holder object storing a
+ * single element.
+ * @author Roberto Tamassia, Michael Goodrich
+ */
+//Copyright (c) 2003 Brown University, Providence, RI
+//Additional modifications and methods by xgiovio
+
+public interface Position<E> {
+
+  E element();
+}
+