message: Update CHANGES.md for v0.21.1
diff: @@ -8,6 +8,15 @@ Rust image aims to be a pure-Rust implementation of various popular image format
  ## Changes
  +### Version 0.21.1
  +
  +- A fairly important bugfix backport
  +- Fixed a potentially memory safety issue in the hdr and tiff decoders, see #885
  +- See [the full advisory](docs/2019-04-23-memory-unsafety.md) for an analysis
  +- Fixes `ImageBuffer` index calculation for very, very large images
  +- Fix some crashes while parsing specific incomplete pnm images
  +- Added comprehensive fuzzing for the pam image types
  +
  ### Version 0.21
  - Updated README to use `GenericImageView`
  