## rotate

### Instructions

In this exercise, if you do not know about it already, you will learn about the rotational cipher "ROT13".

A ROT13 on the Latin alphabet would be as follows:

- Plain: abcdefghijklmnopqrstuvwxyz

- Cipher: nopqrstuvwxyzabcdefghijklm

Your purpose in this exercise is to create a similar `rotate` function that is a better version of the ROT13 cipher.

Your function will receive a `string` and a `number` and it will rotate each letter of that `string` by the `number` of times settled by the second argument towards the right, or towards the left if the number is negative.

Your `function` should only rotate letters. If the string includes punctuation and numbers
they will remain the same.

### Notions

- [patterns](https://doc.rust-lang.org/book/ch18-00-patterns.html)

### Expected functions

```rust
pub fn rotate(input: &str, key: i8) -> String {

}
```

### Usage

Here is a program to test your function.

```rust
use rot::*;

fn main() {

    println!("The letter \"a\" becomes: {}", rotate("a", 26));
    println!("The letter \"m\" becomes: {}", rotate("m", 0));
    println!("The letter \"m\" becomes: {}", rotate("m", 13));
    println!("The letter \"a\" becomes: {}", rotate("a", 15));
    println!("The word \"MISS\" becomes: {}", rotate("MISS", 5));
    println!(
        "The decoded message is: {}",
        rotate("Gur svir obkvat jvmneqf whzc dhvpxyl.", 13)
    );
    println!(
        "The decoded message is: {}",
        rotate("Mtb vznhpqd ifky ozrunsl ejgwfx ajc", 5)
    );
    println!(
        "Your cypher wil be: {}",
        rotate("Testing with numbers 1 2 3", 4)
    );
    println!("Your cypher wil be: {}", rotate("Testing", -14));
    println!("The letter \"a\" becomes: {}", rotate("a", -1));
}
```

And its output:

```console
$ cargo run
The letter "a" becomes: a
The letter "m" becomes: m
The letter "m" becomes: z
The letter "a" becomes: p
The word "MISS" becomes: RNXX
The decoded message is: The five boxing wizards jump quickly.
The decoded message is: Ryg aesmuvi nkpd tewzsxq jolbkc foh
Your cypher wil be: Xiwxmrk amxl ryqfivw 1 2 3
Your cypher wil be: Fqefuzs
The letter "a" becomes: z
$
```