message: Add the readme as a doc-test
  Includes an anonymous extern block at the end of `src/lib.rs` to which
  we link the readme as its documentation, thus making doctest compile and
  run the appropriate sections. A special shoutout to the [doc-comments]
  crate for showing off this technique, that's very clever.
  [doc-comments]:
diff: @@ -109,6 +109,24 @@ mod image;
  mod traits;
  mod utils;
  +// Can't use the macro-call itself within the `doc` attribute. So force it to eval it as part of
  +// the macro invocation.
  +//
  +// The inspiration for the macro and implementation is from
  +// <https://github.com/GuillaumeGomez/doc-comment>
  +//
  +// MIT License
  +//
  +// Copyright (c) 2018 Guillaume Gomez
  +macro_rules! insert_as_doc {
  + { $content:expr } => {
  + #[doc = $content] extern { }
  + }
  +}
  +
  +// Provides the README.md as doc, to ensure the example works!
  +insert_as_doc!(include_str!("../README.md"));
  +
  // Copies data from `src` to `dst`
  //
  // Panics if the length of `dst` is less than the length of `src`.
  