Add debug mode

When enabled, the result will be redirected to a window, and compton
won't take over the screen.

Makes debugging easier.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/config.h

@@ -62,6 +62,8 @@ typedef struct options {
 	// === Debugging ===
 	bool monitor_repaint;
 	bool print_diagnostics;
+	/// Render to a separate window instead of taking over the screen
+	bool debug_mode;
 	// === General ===
 	/// Use the experimental new backends?
 	bool experimental_backends;