A type-safe wrapper from Rust's "slab" data structure
Prevents using slab with obviously wrong keys:
#[macro_use]
extern crate slab_typesafe;
declare_slab_token!(StringHandle1);
declare_slab_token!(StringHandle2);
let mut slab1 : Slab<StringHandle1, _> = Slab::new();
let mut slab2 : Slab<StringHandle2, _> = Slab::new();
let hello = slab1.insert("hello");
let world = slab2.insert("world");
slab1[world]; // the type `Slab<StringHandle1, _>` cannot be indexed by `StringHandle2`
slab2.remove(hello); // expected struct `StringHandle2`, found struct `StringHandle1`
```rust