code: func UniqWithCount() Filter {
  	return FilterFunc(func(arg Arg) error {
  		current := ""
  		count := 0
  		for s := range arg.In {
  			if s != current {
  				if count > 0 {
  					arg.Out <- fmt.Sprintf("%d %s", count, current)
  				}
  				count = 0
  				current = s
  			}
  			count++
  		}
  		if count > 0 {
  			arg.Out <- fmt.Sprintf("%d %s", count, current)
  		}
  		return nil
  	})
  }
docs: // UniqWithCount squashes adjacent identical items in arg.In into a single
  // output prefixed with the count of identical items followed by a space.