Supporting callback like `after_restore` and so on.

[zhouguangming]

We need to support this feature to make code DRY.

[simi]

Good idea @zhouguangming. Would you like to look at this?

[simi]

We can take inspiration from https://github.com/dockyard/destroyed_at/blob/master/lib/destroyed_at.rb#L11.