adds "callback" and "extend" examples

Examples/perl5/extend/example.i

@@ -0,0 +1,20 @@
+/* File : example.i */
+%module(directors="1") example
+%{
+#include "example.h"
+%}
+
+%include "std_vector.i"
+%include "std_string.i"
+
+/* turn on director wrapping for Manager */
+%feature("director") Employee;
+%feature("director") Manager;
+
+/* EmployeeList::addEmployee(Employee *p) gives ownership of the
+ * employee to the EmployeeList object.  The wrapper code should
+ * understand this. */
+%apply SWIGTYPE *DISOWN { Employee *p };
+
+%include "example.h"
+