* Rework the Story Mode UI to display level thumbnails.
* Responsive UI: defaults to wide screen mode and shows 3 levels horizontally
but on narrow/mobile display, shows 2 levels per page in portrait.
* Add "Tiny" screenshot size (224x126) to fit the Story Mode UI.
* Make the pager buttons bigger and more touchable.
* Maximize the game window on startup unless the -w option with a specific
window resolution is provided.
* Add sound effect and music support to Doodle.
* Fix WASM build to use the 'null' sound driver for now.
* Add a Settings button to the main menu; UI for it is WIP.
