Make ImageToTensor compatible with Flux's WHC format

[adrhill]

As discussed in #89 (comment), this PR modifies ImageToTensor to return WHC arrays instead of HWC by default, making it out-of-the box compatible with Flux and Metalhead.jl.

@darsnack's previous suggestion was:

For now, why don't we throw a deprecation warning in ImageToTensor with instructions how to get HWC in the future using (fixed) ImageToTensor + PermuteDims?

However, a release including this PR could be considered breaking since it might break users' existing data preprocessing pipelines.

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Related issues:

• integration with Flux #56 (comment)
• Pre-trained model tutorials don't permute image height and width channels Metalhead.jl#275

[CarloLucibello]

Can you update the version in Project.toml to 0.3?

[adrhill]

I also took the liberty of updating the outdated CHANGELOG.