Count Cache

This create provide a simple way to use a counted cache system. When the count drop to zero, the cache delete the associated key, and the elements cannot be accessed anymore.

Here is an exemple: ```rust use count_cache::CountCache;

fn main() { let ccache = CountCache::new();

ccache.insert("test", 10.256, 2);
assert_eq!(ccache.get(&"test").expect("Err"), 10.256);
assert_eq!(ccache.get(&"test").expect("Err"), 10.256);
assert!(ccache.get(&"test").is_err());
assert!(ccache.get(&"test").is_err());

} ```