Add a Luacheck configuration file and tweak code style

.luacheckrc

@@ -0,0 +1,25 @@
+std = "lua51+minetest"
+unused_args = false
+allow_defined_top = true
+max_line_length = 90
+
+stds.minetest = {
+	read_globals = {
+		"DIR_DELIM",
+		"minetest",
+		"core",
+		"dump",
+		"vector",
+		"nodeupdate",
+		"VoxelManip",
+		"VoxelArea",
+		"PseudoRandom",
+		"ItemStack",
+		"default",
+		table = {
+			fields = {
+				"copy",
+			},
+		},
+	}
+}

init.lua

@@ -11,7 +11,7 @@ minetest.register_ore({
 	ore_type       = "scatter",
 	ore            = "bedrock:bedrock",
 	wherein        = "default:stone",
-	clust_scarcity = 1 * 1 * 1,
+	clust_scarcity = 1,
 	clust_num_ores = 5,
 	clust_size     = 2,
 	height_min     = -30912, -- Engine changes can modify this value
@@ -22,7 +22,7 @@ minetest.register_ore({
 	ore_type       = "scatter",
 	ore            = "bedrock:deepstone",
 	wherein        = "default:stone",
-	clust_scarcity = 1 * 1 * 1,
+	clust_scarcity = 1,
 	clust_num_ores = 5,
 	clust_size     = 2,
 	height_min     = -30656,
@@ -33,7 +33,8 @@ minetest.register_node("bedrock:bedrock", {
 	description = "Bedrock",
 	tile_images = {"bedrock_bedrock.png"},
 	drop = "",
-	groups = {unbreakable = 1, not_in_creative_inventory = 1}, -- For Map Tools' admin pickaxe
+	-- Set `unbreakable` for Map Tools' admin pickaxe
+	groups = {unbreakable = 1, not_in_creative_inventory = 1},
 	sounds = default.node_sound_stone_defaults(),
 })