Composite

Composite

class for "parent-children relation".

method:

initialize(parent): parent is a parent for self.
parent: my parent.
add(c): add a child for self.
delete(c): delete one of my childen.
die: self and children die.
killchildren: children die.
close: die and set "closed" true.
closed?
canclose?: can I close?
showtree(indent=0): print tree. for debug.