coal/helpers.go
func Includes(all, subset []bson.ObjectId) bool {
	for _, item := range subset {
		if !Contains(all, item) {
			return false
		}
	}

	return true
}
func Includes(all, subset []bson.ObjectId) bool {
	for _, item := range subset {
		if !Contains(all, item) {
			return false
		}
	}

	return true
}
// Includes returns true if a list of object ids includes another list of object
// ids.