code: func filterWithLimit(limit uint64) rowFilter {
  	return func(rowID, key uint64, c *roaring.Container) (include, done bool) {
  		if limit > 0 {
  			limit--
  			return true, false
  		}
  		return false, true
  	}
  }
docs: // filterWithLimit returns a filter which will only allow a limited number of
  // rows to be returned. It should be applied last so that it is only called (and
  // therefore only updates its internal state) if the row is being included by
  // every other filter.