Lighter variants of U-Net?

[jbbremnes]

Thanks for the implementation. It would be great if lighter variants also were easily available, for example from 32 down to 128 or 256 channels.

[DhairyaLGandhi]

Nice idea, we can do that by setting up a config that users can tweak at the time of construction. Similar to how the Conv kernel expects a pair in its constructor.