## 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
$
```
