io.go
func ReadLines(reader io.Reader) Filter {
	return FilterFunc(func(arg Arg) error {
		return splitIntoLines(reader, arg)
	})
}
func ReadLines(reader io.Reader) Filter {
	return FilterFunc(func(arg Arg) error {
		return splitIntoLines(reader, arg)
	})
}
// ReadLines emits each line found in reader.