### Storage Engine

A general storage engine, not sure what to pick as the interface

Simpler:
```rust
pub trait StorageEngine { fn store<T: RustcEncodable>(&mut self, t: T); }
```

Probably better?
```rust
pub type PrimaryKey =  &[u8];
pub type SerializedRecord = &[u8];

pub trait StorageEngine {
  fn store<T: Storable>(&mut self, t: T) -> ConstableResult<()>;
}

pub trait Storable {
  fn get_primary_key(&self) -> PrimaryKey;
  fn to_binary(&self) -> SerializedRecord;
  fn from_binary(record: SerializedRecord) -> Self;
}
```