Elevators v2

NOTE: Make sure to delete your config file whenever you update the plugin. Copy the elevators section out of your old config to keep your saved elevators.

New in this version:

• Reloading no longer fails when X or Z is negative.
• Bug fixes with elevator edge detection with negative X and Z.
• Elevator obstacle clearing does not delete other signs in the elevator unless the first line is [elevator] and they're not known to belong to the elevator.
• Streamlined floor coordinate math.