Bukkit

• Made world height adjustable. Set by changing the line in bukkit.yml:

  generator: SkyGrid:<height>
  

  It must be a multiple of 16. If it isn't it will round down to the nearest multiple of 16.

The first spawn for players seems to instantly drop them into the void.  All re-spawns seem to work properly, though.  I need to experiment with multi-world cases to figure out the proper way to avoid this issue.