I've been working on a level editor, that is now available on the beta branch through the Level Select menu > Custom Levels > Import Level. So long as you save the map to the rogueout/maps/custom_levels folder you should be able to select it.
It's experimental though, so make sure you back up the maps you make as they might break as I continue to integrate more features.
There's new SFX and art in the beta branch, along with some more levels.