Look at next jobs to run

Hello,
I'd need to look at the number of the next jobs to run, for example in the next 15 minutes, I did something like this, but I need to loop any job and if they grow up I think it could take too much to run:

```
var from = moment().utc().format('x'),
to = moment().add(15, 'minutes').utc().format('x'),
i = 0;

kue.Job.rangeByType('jobname', 'delayed', 0, -1, 'desc', function(err, jobs) {
if (err) return console.log(err);

_.each(jobs, function(job) {
if (job && job.promote_at) {
var promote = parseInt(job.promote_at, 10);
if (promote > from && promote <= to) i += 1;
}
});
});
```

Is there a better way?

Start with the kue.Job.rangeByType entry point and the delayed-job handling it exposes. Determine whether the existing API can efficiently report jobs promoted within a time window without iterating the full range; done means a supported, documented approach or a clearly scoped API change, with relevant tests.

Written by the indexing model from the issue text.