## roman_numbers_iter
### Instructions
Implement the `IntoIterator` trait for the `RomanNumber` type to enable using a for loop notation. This implementation must allow taking ownership, borrowing and borrowing mutably.
1. Taking ownership (this consumes the RomanNumber)
```rust
for digit in number {
...
}
```
2. Borrowing immutably (this preserves the RomanNumber)
```rust
for digit in & number {
}
```
3. Borrowing mutably (this allow you to modify the RomanNumber without having to return the ownership)
```rust
for digit in & mut number {
}
```
### Notions
- https://doc.rust-lang.org/std/iter/trait.IntoIterator.html
- https://doc.rust-lang.org/std/iter/index.html
### Expected Functions
```rust
use roman_numbers::{RomanDigit, RomanNumber};
impl IntoIterator for & RomanNumber {
}
impl IntoIterator for & mut RomanNumber {
}
impl IntoIterator for RomanNumber {
}
```
### Usage
Here is a program to test your function.
```rust
use roman_numbers::RomanNumber;
fn main() {
let number = RomanNumber::from(15);
for digit in & number {
println!("{:?}", digit);
}
println!("{:?}", number);
}
```
And its output
```console
$ cargo run
RomanNumber([X, X, X, I, I])
RomanNumber([I, X])
RomanNumber([X, L, V])
RomanNumber([Nulla])
$
```
