thread-safe-cache

``` use threadsafecache::*;

let cacheinit: ThreadSafeCache<&str, i32> = ThreadSafeCache::new(); let mut cache1 = cacheinit.clone(); thread::spawn(move || { cache1.put("a", 1); cache1.putexp("b", 2, 1000); }); let mut cache2 = cacheinit.clone(); let t = thread::spawn(move || { sleep(Duration::frommillis(2000)); cache2.rm("a"); cache2.get("b") }); asserteq!(t.join().unwrap(),None);

```