(feature) Problem: Defining the order in which tasks are dequeued is impossible.

[hastebrot]

Proposed solution: Add a new option to WorkerOptions that defines a comparator:

interface WorkerOptions {
  comparator: (item: Task, otherItem: Task) => number
}

Augment Task interface with a running index number.

interface Task {
  id: any,
  priority?: number
  action?: TaskAction
}

Allow to sort the tasks with (task, otherTask) => task.priority - otherTask.priority (accending), and (task, otherTask) => otherTask.priority - task.priority (decending).