`type _ t`````
`val kill : _ t ‑> unit`

kills `t`, which aborts all enqueued jobs that haven't started and all jobs enqueued in the future. If `t` has already been killed, then calling `kill t` has no effect. Note that kill does not affect currently running jobs in any way.

`val is_dead : _ t ‑> bool`

`is_dead t` returns `true` if `t` was killed, either by `kill` or by an unhandled exception in a job.

`val to_limiter : _ t ‑> limiter`

Convert to a limiter