Use std::size_t as argument type for barrier constructor.
Add bounded_queue::upper_bound(), lower_bound(), value_pop().
Make is_empty(), is_full() const.
Add TimePointType template param to push_wait_until(), pop_wait_until().
Change certain [un]bounded_queue method signatures to return queue_op_status.
Their previous signatures didn't provide any way to report a closed queue.
For Note: interruption point, document Throws: fiber_interrupted.
Write a few more words about bounded_queue's high water mark and low water
mark.
