add `get_neighbors` function to api.

mods/bg_api/util_node.lua

@@ -55,3 +55,14 @@ function blockgame.random_walk (data)
 	end
 	return pos
 end
+
+
+
+function blockgame.get_neighbors (pos, neighborhood)
+	neighborhood = neighborhood or blockgame.vector.dirs
+	local neighbors = {}
+	for _, dir in pairs(neighborhood) do
+		table.insert(neighbors, pos + dir)
+	end
+	return neighbors
+end