Now we have callbacks.

There are now 4 callbacks, where can be added how many functions you like on
each one of them:

- Model.beforeSave will fire before INSERT or UPDATE. If returned false, will
  cancel operation.

- Model.afterSave will fire after INSERT or UPDATE. No return value is checked.

- Model.beforeDestroy will fire before DELETE. If returned false, will cancel
  operation.

- Model.afterDestroy will fire after DELETE. No return value is checked.

Each method parameter is a valid INSTANCE function, that must return true or
false, like:

User::beforeSave("before_save");

class User extends TORM\Model {
   public function before_save() {
      return <some condition here>;
   }
}