Remove extern crate declarations from doctests

//! # Example

//!

//! ```rust

//!

//! extern crate openssl;

//!

//! use openssl::rsa::Rsa;

//! use openssl::envelope::Seal;

//! use openssl::pkey::PKey;

//! Generate a 2048-bit RSA public/private key pair and print the public key.

//!

//! ```rust

//!

//! extern crate openssl;

//!

//! use openssl::rsa::Rsa;

//! use openssl::pkey::PKey;

//! use std::str;

//! Generate a 2048-bit RSA key pair and use the public key to encrypt some data.

//!

//! ```rust

//!

//! extern crate openssl;

//!

//! use openssl::rsa::{Rsa, Padding};

//!

//! fn main() {

//! you can create a hasher that you can repeatedly update to add bytes to.

//!

//! ```rust

//! extern crate openssl;

//! extern crate hex;

//!

//! use openssl::sha;

//!

//! fn main() {

//! to the algorithm you want to use.

//!

//! ```rust

//! extern crate openssl;

//! extern crate hex;

//!

//! use openssl::sha::sha256;

//!

//! fn main() {

//! # Example

//!

//! ```rust

//! extern crate openssl;

//!

//! use openssl::x509::extension::BasicConstraints;

//! use openssl::x509::X509Extension;

//!