Use LeveldbOrm + leveldb_key to auto impl trait in leveldb-orm

```rust

[derive(LeveldbOrm)]

[leveldb_key(executable, args)]

struct Command { pub executable: u8, pub args: Vec, pub current_dir: Option, } ```

Generate code

rust impl<'a> leveldb_orm::KeyOrm<'a> for Command { type KeyType = (u8, Vec<String>); type KeyTypeRef = (&'a u8, &'a Vec<String>); #[inline] fn key( &self, ) -> std::result::Result<leveldb_orm::EncodedKey<Self>, Box<dyn std::error::Error>> { Self::encode_key((&self.executable, &self.args)) } }