module Root:sig..end
val create : 'a -> unit Ctypes.ptrcreate v allocates storage for the address of the OCaml value v,
registers the storage as a root, and returns its address.
val get : unit Ctypes.ptr -> 'aget p retrieves the OCaml value whose address is stored at p.
val set : unit Ctypes.ptr -> 'a -> unitset p v updates the OCaml value stored as a root at p.
val release : unit Ctypes.ptr -> unitrelease p unregsiters the root p.