Minor refactor

- Use init() function to set up commands
- Expose an Execute() function instead of the root command

main.go

@@ -8,9 +8,8 @@ import (
 )
 
 func main() {
-	cmd := cli.NewRootCmd()
-	if err := cmd.Execute(); err != nil {
-		fmt.Println(err)
+	if err := cli.Execute(); err != nil {
+		fmt.Fprint(os.Stderr, err)
 		os.Exit(1)
 	}
 }