Renamed PropertyChangedNotifier to ObservableObject (like ObservableCollection).
- Renamed test namespace to match recent change.
- Changed default change comparison to use EqualityComparer<T>.
- Refactored FileInfoPathEqualityComparer to work with FileSystemInfo.
- Removed ObservableObject<T> and moved expression methods to overloads on ObservableObject.
Added convenience equality extension methods for PropertyBuilder.