Corrected types of variables, updated Cargo file, removed unused import

This should make it build with the latest version of Rust.

* The latest version of Cargo prefers [lib] to [[lib]], so I've made this change
* MAX_SEGMENTS and NUM_DCT_TOKENS are only used after being cast to uints, so I've changed their types.
* CloneableIterator was never actually used, so I've dropped it.