[Teton] Draw a green square into the framebuffer.

sys/teton/framebuffer/framebuffer.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <yellowstone/yellowstone.yunq.h>
+
+class Framebuffer {
+ public:
+  Framebuffer(const FramebufferInfo& info);
+
+  void DrawPixel(uint32_t row, uint32_t col, uint32_t pixel);
+
+ private:
+  // FIXME: Implement Yunq copy or move so we
+  // don't have to store a reference here.
+  const FramebufferInfo& fb_info_;
+  uint32_t* fb_;
+};