code: function (subscriptions, fn, context) {
    for (var id in subscriptions) {
      for (var property in subscriptions[id]) {
        fn.call(context, subscriptions[id][property], property, id);
      }
    }
  }
docs: Iterate over a subscriptions object, calling a function with the object
  property details and a unique callback function.
  
  @param {Array}    subscriptions
  @param {Function} fn
  @param {Function} callback