* The default AD engine has switched from [Tracker to Zygote.jl](https://github.com/FluxML/Flux.jl/pull/669)
- The dependency on Tracker.jl has been removed.
- This means Flux now does not depend on using a specialised `TrackedArray` type, and can be used with normal Array implementations directly.
- Tracker compatibility is maintained in most common cases, but Zygote will be the preferred AD backend for Flux from now on.
* The CUDNN wrappers have been [moved from Flux into CuArrays](https://github.com/FluxML/Flux.jl/pull/874), to allow for better supporting the CUDA backend, and improve user experience, not to mention making Flux lean.
*`*crossentropy` functions now [work as expected with CuArrays](https://github.com/FluxML/Flux.jl/pull/926). [PR for binarycrossentropy](https://github.com/FluxML/Flux.jl/pull/940).
* Added [clearer docs](https://github.com/FluxML/Flux.jl/pull/904) around training and the Optimiser interface.
* [Layer initialisations](https://github.com/FluxML/Flux.jl/pull/937) have been improved with a clearer API on how to extend it for other purposes.
* [Better messaging around CUDA availability](https://github.com/FluxML/Flux.jl/pull/924), with hooks to initialize the GPU as default where possible.
* New [InstanceNorm](https://github.com/FluxML/Flux.jl/pull/634), as popularized by [Instance Normalization: The Missing Ingredient for Fast Stylization](https://arxiv.org/abs/1607.08022).