[Feat] Having a kornia.nn module to include all module-like APIs.

Currently, most APIs are scattered in different files. Also, we are mixing the functional APIs and module-like APIs. Should we have a kornia.nn to split the module-like APIs out of functional ones?

• For a simple starter, we may have only __init__.py inside the kornia.nn to create a shortcut for users. To have something like:

  from kornia.augmentation import (
      RandomHorizontalFlip,
      RandomVerticalFlip,
      RandomErasing,
      RandomGrayscale,
      ColorJitter,
      RandomRotation,
      RandomCrop,
      RandomResizedCrop,
  )
  from kornia.color.normalize import (
      Normalize,
      Denormalize
  )
  from kornia.gray import (
      RgbToGrayscale,
      BgrToGrayscale
  )
  ...
  

• Eventually, to have a file structure like below to separate those two different APIs:

  • kornia
    • nn
      • agumentation
      • color
      • feature
      • filters
      • geometry
    • augmentation
    • color
    • feature
    • filters
    • geometry

[edgarriba]

@yutayamazaki yes, please go ahead. Just we need to take care about potential cycle dependencies. /cc @shijianjian

[shijianjian]

I am thinking to resume this given the needs of using Kornia preprocessing/augmentation/operation as layers.

More or less, at least to have a summary list like:

Operation	Diffrentiable	JIT	ONNX
GrayToRGB	Y	Y	Y
Equalize	N	Y	Y
Affine	Y	Y	N