Added geo and gl packages from gogeline and improved documentation.

game.go

@@ -67,6 +67,7 @@ func Run(game Game, options *RunOptions) {
 
 	for running {
 		if exitOnClose && wnd.ShouldClose() {
+			cleanup()
 			return
 		}
 
@@ -87,3 +88,9 @@ func Run(game Game, options *RunOptions) {
 func Stop() {
 	running = false
 }
+
+func cleanup() {
+	for _, system := range systems {
+		system.Cleanup()
+	}
+}