AMDs contrast adaptive sharpening as hook

[BenjaminWegener]

from https://gist.githubusercontent.com/kevinlekiller/2ff6d0222fe6dcd81d63fd11e73ff9d1/raw/8ad007cf4de27e16d5c96b40cefe50ea08516984/CAS.glsl

[bjin]

Thanks for interests on this project.

Note that:

1. This repo does not try to collect every mpv shaders. What's more, since copyright is concerned. PR from original author is prefered, or at least with explicit permission (relicense to GPLv3 included).
2. This repo currently only contains prescalers. Sharpeners are post processing shaders and are basically unrelated.
3. It should be better integrated with mpv. For example, use mpv internal linear srgb conversion with custom hooks.

Closing.