code: func help(args []string) {
  	if len(args) == 0 {
  		printUsage(os.Stdout)
  		return
  	}
  	if len(args) != 1 {
  		fmt.Fprintf(os.Stderr, "usage: gvt help command\n\nToo many arguments given.\n")
  		os.Exit(2)
  	}
  
  	arg := args[0]
  
  	// 'gvt help documentation' generates alldocs.go.
  	if arg == "documentation" {
  		var u bytes.Buffer
  		printUsage(&u)
  		f, _ := os.Create("alldocs.go")
  		tmpl(f, documentationTemplate, struct {
  			Usage    string
  			Commands []*Command
  		}{
  			u.String(),
  			commands,
  		})
  		f.Close()
  		return
  	}
  
  	for _, cmd := range commands {
  		if cmd.Name == arg {
  			tmpl(os.Stdout, helpTemplate, cmd)
  			return
  		}
  	}
  
  	fmt.Fprintf(os.Stderr, "Unknown help topic %#q. Run 'gvt help'.\n", arg)
  	os.Exit(2)
  }
docs: // help implements the 'help' command.