Region Vision v1.2

• Updated for the Terraria Server API version 1.17.
• I now use the RegionDeleted hook to inform users immediately and descriptively when a region they are viewing is deleted. It turns out I can't use RegionEntered and RegionLeft, because they don't work when regions overlap.
• The /rv command now shows how far away the border is if the region is large. (For smaller regions, you can just use /region tp.)