* ToggleTree

* Comply with ruby's allocation framework.
  * All widgets have `initialize' method.
  * `initialize' method creates the target widget.
  * (ruby-1.6) Implement rb_fltk_class_new_instance()
               which is called by `new' method.
    (ruby-1.7) Get rid of `new' method from widget classes.
  * Get rid of rb_obj_call_init().

* FLVW: http://flvw.sourceforge.net/

* FLEK: http://www.carambadesigns.com/flek/
