Cache library to be used in async or singlethreaded(not implemented) context.
``` use std::sync::Arc; use rusticache::AsyncCache; use std::time::Duration;
async fn dostuff() { let cache = Arc::new(AsyncCache::new( Duration::fromsecs(10), Box::new(|| Ok(String::from("This is Sparta!"))) ));
let data = cache.get_data().await;
assert_eq!(*data.unwrap(), String::from("This is Sparta!"));
} do_stuff(); ```