approve() says yes, deny() says no (the model is told the person did
not allow the call, and why). Give it the approval event a stream's
.each received (the call waiting in this session goes on), or a turn
that waits: a conversation's turn goes on when nothing else waits for an
answer, here, and its answer is returned (resume = FALSE: later, with
resume_turn()).
Usage
approve(x, approval = NULL, by = NULL, resume = TRUE)
deny(x, approval = NULL, reason = NULL, by = NULL, resume = TRUE)