This module provides a way to deal with self-referential data.
The main idea is to allocate such data in a generator frame and then give access to it by executing user-provided closures inside that generator. The module provides a safe abstraction for the latter task.
The interface consists of two exported macros meant to be used together:
declare_box_region_typewraps a generator inside a struct with
accessmethod which accepts closures.
box_region_allow_accessis a helper which should be called inside a generator to actually execute those closures.