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.

Example

    let db: sled::Db = sled::open("db")?;
    let animals = typed_sled::Tree<String, Animal>::init(&db, "animals")
    tree.insert("Larry", Animal::Dog)?;

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