AES Module level docs and example

//! create a new key with [`new_encrypt`] and perform an encryption/decryption

//! using that key with [`aes_ige`].

//!

//! AES is a 128-bit (16 byte) block cipher.  The rust implmentation will panic

//! if the input or output does not meet this 16-byte boundry.  Attention must

//! be made in this low level implementation to pad the value to the 128-bit boundry.

//!

//! [`new_encrypt`]: struct.AesKey.html#method.new_encrypt

//! [`aes_ige`]: fn.aes_ige.html

//!

//! ```rust

//! # extern crate openssl;

//! extern crate hex;

//! use openssl::aes::{AesKey, KeyError};

//! use hex::FromHex;

//! use openssl::aes::{AesKey, KeyError, aes_ige};

//! use openssl::symm::Mode;

//! use hex::{FromHex, ToHex};

//!

//! fn decrypt() -> Result<(), KeyError> {

//!   let raw_key = "000102030405060708090A0B0C0D0E0F";

//!    let key = AesKey::new_encrypt(&Vec::from_hex(raw_key).unwrap())?;

//!   let hex_cipher = "12345678901234561234567890123456";

//!   let randomness = "000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F";

//!   if let (Ok(key_as_u8), Ok(cipher_as_u8), Ok(mut iv_as_u8)) =

//!       (Vec::from_hex(raw_key), Vec::from_hex(hex_cipher), Vec::from_hex(randomness)) {

//!     let key = AesKey::new_encrypt(&key_as_u8)?;

//!     let mut output = vec![0u8; cipher_as_u8.len()];

//!     aes_ige(&cipher_as_u8, &mut output, &key, &mut iv_as_u8, Mode::Encrypt);

//!     assert_eq!(output.to_hex(), "a6ad974d5cea1d36d2f367980907ed32");

//!   }

//!   Ok(())

//! }

//!