Sled with Types instead of Bytes

This crate builds on top of [sled] and it's api is identical, except that it uses types in all places where sled would use bytes or it's IVec type. Types are binary encoded using bincode.

Example

```rust let db: sled::Db = sled::open("db")?;

// The id is used by sled to identify which Tree in the database (db) to open.
let animals = typed_sled::Tree::<String, Animal>::open(&db, "unique_id");

let larry = "Larry".to_string();
animals.insert(&larry, &Animal::Dog)?;

assert_eq!(animals.get(&larry)?, Some(Animal::Dog));

```

Not tested throughoutly, in particular the Subscriber api might not be implemented correctly.