Allow arguments to the default command

I.e. `remind today` is equivalent to `remind list today` now.

go/remind/remind.go

func init() {
	flag.BoolVar(&flags.showAll, "all", false, "Show all reminders")
func isCommand(s string) bool {
	return s == "list" || s == "l" || s == "add"
}
func main() {
	flag.Parse()
	start := 0
	cmd := "list"
	if flag.NArg() >= 1 {
	if flag.NArg() >= 1 && isCommand(flag.Arg(0)) {
		start = 1
		cmd = flag.Arg(0)
	}
	}
	switch cmd {
	case "add":
		if flag.NArg() != 3 {
			flag.Usage()
			os.Exit(1)
		}
		date, err := parseTime(flag.Arg(1))
		if err != nil {
			exit(err)
		}
		description := flag.Arg(2)
		reminders = append(reminders, Reminder{Date: date, Description: description})
		needWrite = true
	case "list", "l":
		fallthrough
	default:
		min := time.Now()
		max := min.AddDate(0, 0, 7)
		if flag.NArg() > 1 {
			switch flag.Arg(1) {
		if flag.NArg() > start {
			switch flag.Arg(start) {
			case "today":
				min = truncateHours(time.Now())
				max = min.Add(24 * time.Hour)
			default:
				fmt.Fprintf(os.Stderr, "unknown command '%s'\n", cmd)
				os.Exit(1)
			}
		}
				fmt.Printf("%s - %s\n", r.Date, r.Description)
			}
		}
	case "add":
		if flag.NArg() != 3 {
			flag.Usage()
			os.Exit(1)
		}
		date, err := parseTime(flag.Arg(1))
		if err != nil {
			exit(err)
		}
		description := flag.Arg(2)
		reminders = append(reminders, Reminder{Date: date, Description: description})
		needWrite = true
	default:
		fmt.Fprintf(os.Stderr, "unknown command '%s'\n", cmd)
		os.Exit(1)
	}
	if needWrite {