Feature: minkowski distance and related mae, mse, psnr, etc

[johnnychen94]

These functions are widely used in image quality assessment for the purpose of benchmarking image algorithms, also used to train neural networks.

• mae, mse (distance)
• psnr, ssim (image quality assessment) -- perhaps in the future we need a separate repo, but for now it's best put here.

There's an unfinished PR: https://github.com/JuliaImages/ImageDistances.jl/pull/6

Blocking issue:

• [ ] https://github.com/JuliaImages/ImageDistances.jl/issues/17

I opened this issue as a memo.

[johnnychen94]

The unfinished part of this issue now belongs to ImageQualityIndex

So we can close this now