move item_matches into api.

move function `item_matches` from `bg_crafting` into `bg_api`, since
it'll be useful in many other places.

mods/bg_api/init.lua

@@ -13,6 +13,7 @@ load_file("util_random")
 load_file("util_vector")
 
 load_file("util_node")
+load_file("util_item")
 
 load_file("wrappers")
 

mods/bg_api/util_item.lua

@@ -0,0 +1,12 @@
+function blockgame.item_matches (name, options)
+	return blockgame.any(options, function (option)
+		if name == option then return true end
+
+		if blockgame.starts_with(option, "group:") then
+			local group = string.sub(option, 7)
+			return minetest.get_item_group(name, group) > 0
+		end
+
+		return false
+	end)
+end

mods/bg_crafting/pummel.lua

@@ -1,5 +1,9 @@
 local api = blockgame.crafting
 
+-- LOCALS
+
+local matches = blockgame.item_matches
+
 -- pummeling is heavily based on nodecore by Warr1024 (both the mechanic itself and the code here implementing it).
 
 local pummel_recipes = {}
@@ -21,22 +25,10 @@ function api.register_pummel_recipe (def)
 	table.insert(api.registered_recipes, def)
 end
 
--- TODO: extract this function into general api
-local function item_matches (nodename, options)
-	return blockgame.any(options, function (option)
-		if nodename == option then return true end
-		if blockgame.starts_with(option, "group:") then
-			local group = string.sub(option, 7)
-			return minetest.get_item_group(nodename, group) > 0
-		end
-		return false
-	end)
-end
-
 -- TODO: add support for pummel recipes using groups instead of just specific node names.
 function api.pummel_check (pos, used, target_node)
 	for _, def in pairs(pummel_recipes) do
-		if item_matches(used, def.used) and item_matches(target_node.name, def.target) then
+		if matches(used, def.used) and matches(target_node.name, def.target) then
 			if type(def.check) == "function" and not def.check(pos, used, target_node) then
 				return false
 			end