Clean up crafting recipes, add new helpers

mods/3d_armor/3d_armor/armor.conf

@@ -1,6 +1,6 @@
 -- Armor Configuration
 ARMOR_MATERIALS = {
-	leather = "group:wood",
+	leather = "mobs:leather",
 	iron = "default:steel_ingot",
 	chain = nil,
 	gold = "default:gold_ingot",

mods/3d_armor/3d_armor/init.lua

@@ -150,8 +150,7 @@ minetest.register_tool("3d_armor:boots_chain", {
 -- Register Craft Recipies
 
 local craft_ingreds = {
-	-- FIXME: Replace with leather
-	leather = { "default:wood" },
+	leather = { "mobs:leather" },
 	steel = { "default:steel_ingot", "default:iron_nugget" },
 	gold = { "default:gold_ingot", "default:gold_nugget" },
 	diamond = { "default:diamond" },