message: Changelog for 0.31.0
diff: # Changelog
  +## Version 0.31 (2021-12-11)
  +
  +- Updated glutin to version 0.31.0. See the glutin release notes [here](https://github.com/rust-windowing/glutin/blob/master/CHANGELOG.md#version-0280-2021-12-02).
  +- Use mdbook for the book.
  +
  ## Version 0.30.2 (2021-09-06)
  - Added depth and stencil buffer blitting.
  