## order_books
### Instructions
Build a module called `library` with two sub-modules inside of it:
- `writers` which contains a structure called `Writer` which has a first_name (String),a last_name (String) and a set of books (Vec\<Book\>).
- `books` which contains a structure called `Book` which has a title (String) and a year of publication (u64).
A function `order_books` also has to be created (outside the previous modules which receives a writer (Writer) and orders the set of books alphabetically.
### Expected Functions and Structs
#### (The structs declarations need to be filled and added in the appropriate submodules)
```rs
pub struct Writer {
}
```
```rs
pub struct Book {
}
```
```rs
pub fn order_books(writer: & mut Writer) {
}
```
### Example
Here is a program to test your function and structs:
```rs
pub use library::writers::Writer;
pub use library::books::Book;
fn main() {
let mut writer_a = Writer {
first_name: "William".to_string(),
last_name: "Shakespeare".to_string(),
books: vec![
Book {
title: "Hamlet".to_string(),
year: 1600,
},
Book {
title: "Othelo".to_string(),
year: 1603,
},
Book {
title: "Romeo and Juliet".to_string(),
year: 1593,
},
Book {
title: "MacBeth".to_string(),
year: 1605,
},
],
};
println!("Before ordering");
for b in & writer_a.books {
println!("{:?}", b.title);
}
order_books(& mut writer_a);
println!("\nAfter ordering");
for b in writer_a.books {
println!("{:?}", b.title);
}
}
```
And its output:
```sh
$ cargo run
Before ordering
"Hamlet"
"Othelo"
"Romeo and Juliet"
"MacBeth"
After ordering
"Hamlet"
"MacBeth"
"Othelo"
"Romeo and Juliet"
$
```
