code: def migration(self, from_ver: int, to_ver: int):
          
          def decorator(func):
              migration = Migration(from_ver, to_ver, func)
              self.register_migration(migration)
              return func
          return decorator
docs: Decorator to create and register a migration.
  
          >>> manager = MigrationManager()
          >>> @manager.migration(0, 1)
          ... def migrate(conn):
          ...     pass