* implement method to upgrade NPCs to next-higher tier without slaying
them
* decrease efficiency of fish-farm harvesting (decreased chance of catch
by 50%)
* tree farm puts apples in as a resource
* remove ability to pickup items from ground (uneeded, and annoying)
* disable npc collision with other npcs (should remove door cluster
issues)
* adjust npc pathfinding to explicitly remove cactus as a pathable block
* add recipes for iron rings and iron rings -> chain mail