Simple local in-memory cache for Rust.
```rust use memory_cache::MemoryCache; use std::time::Duration;
let scanfrequency = Duration::fromsecs(60);
let mut cache = MemoryCache::new(scan_frequency);
let key: &'static str = "key"; let value: &'static str = "Hello, World!"; let expiration = Duration::from_secs(30);
cache.set(key, value, Some(expiration));
let cached_value = cache.get(&key);
asserteq!(cachedvalue, Some(&value)); ```