## roman_numbers
### Instructions
Implement the `From<u32>` trait to create a roman number from a number. The roman number should be in subtractive notation (the common way to write roman number I, II, III, IV, V, VI, VII, VIII, IX, X ...).
Start by defining the digits as `RomanDigit` (`Nulla` is 0).
Next define `RomanNumber` as a wrapper to a vector of `RomanDigit` , and implement the Trait `From<u32>` .
### Expected Functions and Data Structures
```rust
use crate::RomanDigit::*;
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum RomanDigit {
Nulla,
I,
V,
X,
L,
C,
D,
M,
}
#[derive(Debug, Clone, Debug, PartialEq, Eq)]
pub struct RomanNumber(pub Vec< RomanDigit > );
impl From< u32 > for RomanDigit {
}
impl From< u32 > for RomanNumber {
}
```
### Usage
Here is a program to test your function.
```rust
use roman_numbers::RomanNumber;
fn main() {
println!("{:?}", RomanNumber::from(32));
println!("{:?}", RomanNumber::from(9));
println!("{:?}", RomanNumber::from(45));
println!("{:?}", RomanNumber::from(0));
}
```
And its output:
```console
$ cargo run
RomanNumber([X, X, X, I, I])
RomanNumber([I, X])
RomanNumber([X, L, V])
RomanNumber([Nulla])
$
```
