109.08.00

- Added module `Async.Command`
  This is `Core.Command` with additional async functions.  In particular
  it contains a function `async_basic` that is exactly the same as
  `Core.Command.basic`, except that the function it wraps returns
  `unit Deferred.t`, instead of `unit`.  `async_basic` will also start the
  async scheduler before the wrapped function is run, and will stop the
  scheduler when the wrapped function returns.