DRM Support

[FLimburg]

Feature Request: DRM or headless support #352

• Added new dependency: drm
• Created new feature: drm
• Refactored the rendering pipeline from window/rendering.rs into a separate function for reuse
• Added new mod: drm
  • card.rs for handling the device opening
  • display_thread.rs for async copying over to drm buffer
  • drm_canvas.rs as drm replacement of the normal canvas
  • drm_window.rs to handle drm device and canvas creation
• created some drm examples for testing.

Works for me on a raspberry pi4 with a 1240*600 pixel display.