Feature Request: DRM or headless support

[FLimburg]

For systems that have no window manager it would be nice to have support for direct rendering manager. Or if easier at first a headless mode that would allow to use kiss3d with existing drm crates like https://github.com/Smithay/drm-rs

What would be a viable approach? Write a drm compatible canvas or window implementation?

[FLimburg]

Started to experiment with this:
FLimburg#1

So far I have

• introduced a feature drm
• created a headless mode without need for winit by
  • creating drm_window
  • creating drm_canvas
• added drm_cube example for testing, it will safe every 24th frame as a screenshot instead of showing anything.

It compiles on my console only raspberry pi without wayland and winit and executes successfully.

Next I would try to get actual drm in there.

Looking for some feedback, like does this approach make any sense for the general architecture or future plans of kiss3d?