Add Travis CI and LuaCheck (#5)

.luacheckrc

@@ -0,0 +1,15 @@
+unused_args = false
+allow_defined_top = true
+max_line_length = 999
+
+globals = {
+    "minercantile",
+}
+
+read_globals = {
+    string = {fields = {"split", "trim"}},
+    table = {fields = {"copy", "getn"}},
+
+    "minetest", "ItemStack",
+    "default", "unified_inventory",
+}