CAST5 block cipher.

Implementation according to RFC 2144.

Usage example

use cast5::block_cipher_trait::generic_array::GenericArray;
use cast5::block_cipher_trait::BlockCipher;
use cast5::Cast5;

let key = GenericArray::from_slice(&[0u8; 16]);
let mut block = GenericArray::clone_from_slice(&[0u8; 8]);
// Initialize cipher
let cipher = Cast5::new(&key);

let block_copy = block.clone();
// Encrypt block in-place
cipher.encrypt_block(&mut block);
// And decrypt it back
cipher.decrypt_block(&mut block);
assert_eq!(block, block_copy);