sled 0.16.5

`sled` is a flash-sympathetic persistent lock-free B+ tree. # Examples ``` let t = sled::Tree::start_default("my_db").unwrap(); t.set(b"yo!", b"v1".to_vec()); assert!(t.get(b"yo!").unwrap().unwrap() == &*b"v1".to_vec()); t.cas( b"yo!", // key Some(b"v1"), // old value, None for not present Some(b"v2".to_vec()), // new value, None for delete ).unwrap(); let mut iter = t.scan(b"a non-present key before yo!"); // assert_eq!(iter.next(), Some(Ok((b"yo!".to_vec(), b"v2".to_vec())))); // assert_eq!(iter.next(), None); t.del(b"yo!"); assert_eq!(t.get(b"yo!"), Ok(None)); ```