Added VGA grayscale and choose screen type

VGA render can transform to grayscale and applying color.
Green, amber and white.

src/config.c

@@ -804,7 +804,7 @@ static void loadconfig_general(void)
 	}
 	enable_overscan = !!config_get_int(cat, "enable_overscan", 0);
 	vid_cga_contrast = !!config_get_int(cat, "vid_cga_contrast", 0);
-
+	video_grayscale = config_get_int(cat, "video_grayscale", 0);
 
         window_remember = config_get_int(cat, "window_remember", 0);
 
@@ -1801,6 +1801,15 @@ static void saveconfig_general(void)
 	        config_set_int(cat, "vid_cga_contrast", vid_cga_contrast);
 	}
 
+	if (video_grayscale == 0)
+	{
+		config_delete_var(cat, "video_grayscale");
+	}
+	else
+	{
+	        config_set_int(cat, "video_grayscale", video_grayscale);
+	}
+
 
 	if (window_remember)
 	{