Fix doc test and move external documentation link to rand_bytes function

//! Cryptographically strong random bytes.

//!

//! This module exposes functionality to put cryptographically strong

//! pseudo-random bytes into a buffer.

//! Utilities for secure random number generation.

//!

//! # Examples

//!

//! To generate a buffer with cryptographically strong bytes:

//!

//! ```

//! let muf buf = [0; 256];

//! use openssl::rand::rand_bytes;

//!

//! let mut buf = [0; 256];

//! rand_bytes(&mut buf).unwrap();

//! ```

//!

//! # External OpenSSL Documentation

//!

//! [RAND_bytes](https://www.openssl.org/docs/man1.1.0/crypto/RAND_bytes.html)

use libc::c_int;

use ffi;

use error::ErrorStack;

/// Fill buffer with cryptographically strong pseudo-random bytes.

///

/// # Examples

///

/// To generate a buffer with cryptographically strong bytes:

///

/// ```

/// use openssl::rand::rand_bytes;

///

/// let mut buf = [0; 256];

/// rand_bytes(&mut buf).unwrap();

/// ```

///

/// # External OpenSSL Documentation

///

/// [RAND_bytes](https://www.openssl.org/docs/man1.1.0/crypto/RAND_bytes.html)

pub fn rand_bytes(buf: &mut [u8]) -> Result<(), ErrorStack> {

    unsafe {

        ffi::init();