## rot13

### Instructions

Write a program that takes a `string` and displays it, replacing each of its
letters by the letter 13 spaces ahead in alphabetical order.

-   'z' becomes 'm' and 'Z' becomes 'M'. Case remains unaffected.

-   The output will be followed by a newline (`'\n'`).

-   If the number of arguments is different from 1, the program displays a newline (`'\n'`).

### Usage

```console
student@ubuntu:~/piscine-go/test$ go build
student@ubuntu:~/piscine-go/test$ ./test "abc"
nop
student@ubuntu:~/piscine-go/test$ ./test "hello there"
uryyb gurer
student@ubuntu:~/piscine-go/test$ ./test

student@ubuntu:~/piscine-go/test$
```