Changes:

• the level selection screen is now scrollable, so you can have infinite amounts of levels (as long as you don't eat up all the disk space of course)
• the "Render level" and "Render chunk" buttons in the pause menu now work, and do exactly that with a nice progress screen
• some debug messages got removed
• ore blocks got added
• cactus can only be placed on sand (or an another cactus) with no blocks next to it; otherwise it breaks
• added the flat level type
• added the ability to select level type when creating a new world; all worlds from earlier versions will be converted to the overworld one