pub fn contains_key<K: AsRef<[u8]>>(&self, key: K) -> io::Result<bool> {
        self.get(key).map(|v| v.is_some())
    }
Returns `true` if the `Tree` contains a value for
the specified key.

# Examples

```
# fn main() -> Result<(), Box<dyn std::error::Error>> {
# let config = sled::Config::tmp().unwrap();
# let db: sled::Db<1024> = config.open()?;
db.insert(&[0], vec![0])?;
assert!(db.contains_key(&[0])?);
assert!(!db.contains_key(&[1])?);
# Ok(()) }
```
src/tree.rs