This is the javascript equivalent of Async_unix.Scheduler, ie a reimplementation of the async scheduler for javascript (at least the part of it that makes sense).

`val sleep : float ‑> unit Async_kernel.Deferred.t`

`sleep d` is a deferred which becomes determined in `d` seconds.

`val yield : unit ‑> unit Async_kernel.Deferred.t`

`yield ()` returns a deferred that becomes determined after the current cycle completes.

`val init : unit ‑> unit`

Initialize the async scheduler

`val initialized : unit ‑> bool`