async_init

init object asynchronously without Arc

```rust

[async_init]

pub async fn getdbpool() -> Result { println!("thread id is {:?}, create mysql pool", thread::current().id()); let dburl = env::var("DATABASEURL").expect("DATABASE_URL must be set to run this app"); let pool:MySqlPool = Pool::new(&db_url).await?; Ok(pool) } ```