Changes:

• changed the generator button to "Generator: X" instead of just "X"
• optimized the options mechanism
• added the options screen
• added gravel
• tree leaves break when the stem got destroyed. Player-placed leaves don't decay
• sand and gravel fall when there is no block beneath

WARNING: This release introduces the level format 8, which is incompatible with the previous one. If you try to load an older world in this version, it will get regenerated, so don't do that!