You can now save your game within a dungeon! Any progress within the current dungeon will be lost, but you can continue your crawl at a later time. Saved crawls are also synced to the Steam Cloud.
To save your crawl, access the pause menu and select 'Save & Quit'. Note that you can only save once at least 1 dungeon has been completed.
From the title, if you have a saved crawl, the 'Play' button is replaced with 'Continue'.