Arthur published yesterday the 6th draft of the srfi-167 (okvs) specification.

Here are the changes:

- Two libraries are specified `okvs` and `engine`

- `engine` is an extended version of the record that was defined in
SRFI-168. This will allow users to implement layers in a portable way.
See https://srfi.schemers.org/srfi-167/srfi-167.html#engine

- manual transaction management procedure are gone

- There is now a (make-default-state) that returns the default state
of the transaction

- hooks were added, see https://srfi.schemers.org/srfi-167/srfi-167.html#hooks