sdl: separate sdl module into multiple, dependent submodules

vlib/sdl/examples/basic_window/main.v

@@ -0,0 +1,31 @@
+module main
+
+import sdl
+
+fn main() {
+	C.SDL_Init(C.SDL_INIT_VIDEO)
+	window := C.SDL_CreateWindow('Hello SDL2', 300, 300, 500, 300, 0)
+	renderer := C.SDL_CreateRenderer(window, -1, C.SDL_RENDERER_ACCELERATED | C.SDL_RENDERER_PRESENTVSYNC)
+
+	mut should_close := false
+	for {
+		ev := sdl.Event{}
+		for 0 < sdl.poll_event(&ev) {
+			match int(ev._type) {
+				C.SDL_QUIT { should_close = true }
+				else {}
+			}
+		}
+		if should_close {
+			break
+		}
+
+		C.SDL_SetRenderDrawColor(renderer, 255, 55, 55, 255)
+		C.SDL_RenderClear(renderer)
+		C.SDL_RenderPresent(renderer)
+	}
+	
+	C.SDL_DestroyRenderer(renderer)
+	C.SDL_DestroyWindow(window)
+	C.SDL_Quit()
+}