More TODOs.

todo.md

@@ -9,6 +9,7 @@ ALL:
 		*(d.(*bool)) = true
 		ui.Stop <- struct{}{}
 ```
+- implement the concept of closing a window (which renders it unavilable for future use) and make it part of the Closing documentation
 
 MAC OS X:
 - NSComboBox scans the entered text to see if it matches one of the items and returns the index of that item if it does; find out how to suppress this so that it returns -1 unless the item was chosen from the list (like the other platforms)