Reference-counted fat pointers that contain both an owning std Rc (or Arc) and a pointer to a field owned by that Rc. This is a "self-referential" type in the vein of ouroboros or yoke.

By specializing just for the reference-counted pointers, this crate provides a much simpler API compared to that of ouroboros, yoke, or any other crate for general self-referential types.