make a database connection with rust, diesdel and sqlite.

use diesel::prelude::*;
use diesel::sqlite::SqliteConnection;
use r2d2::{self, Pool};
use r2d2_diesel::ConnectionManager;

pub fn init_pool(database_url: &str) -> Pool<ConnectionManager<SqliteConnection>> {
    let manager = ConnectionManager::<SqliteConnection>::new(database_url);
    r2d2::Pool::builder()
        .build(manager)
        .expect("Failed to create pool")
}