Added unload texture function

Raylib is written in C, so cleaning up resources (such as textures, images, or sounds) must be done manually

src/main.cpp

@@ -27,7 +27,8 @@ int main()
         EndDrawing();
     }
 
-    CloseWindow();
+    UnloadTexture(texture);
 
+    CloseWindow();
     return 0;
 }