message: pnet_macros: doctest can now compile and run
diff: //! specify the format of on-the-wire packets, and automatically generate zero-copy accessors and
  //! mutators for the fields. It is used as follows:
  //!
  -//! ```ignore
  -//!
  -//! extern crate pnet_macros_support;
  -//!
  +//! ```
  +//! /// Import the #[packet] custom attribute
  +//! use pnet_macros::packet;
  //! /// This module contains a list of type aliases which may be used
  //! use pnet_macros_support::types::{u4, u12be};
  //!
  //! #[payload]
  //! payload: Vec<u8>
  //! }
  -//!
  -//! # fn main(){}
  //! ```
  //! A number of things will then be generated. You can see this in action in the documentation and
  //! source of each of the packet types in the `pnet::packet` module. Things generated include
  