gbdb,video: improve logging

Add more runtime toggles and add the ability to log to a file for
faster runs and better searchability.

src/gbemu/video.h

@@ -92,6 +92,7 @@ struct gb_video {
 	/******************************/
 
 	int line_counter;
+	int debug_logging;
 
 	struct gb_memory *memory;
 };