add permission to change convertion functions of model and view, which could supply different convertion strategies to view change event and model change event.
get stable objects from gtk.
permit filename tobe None when do not use auto load in View.
use instance name as ops's get and set function's parameter to solve the problem that view instance will crash in several view objects, same type.
add property to class just one time when there is several objects in the same class.
change all convertion name to conversion
try to use unidir binding to bind single element.
signal is now works.