Added all SEPA countries (IBANs from European Union countries) and minimal test coverage for countries

lib/iban_ex/country/lu.ex

@@ -1,6 +1,13 @@
 defmodule IbanEx.Country.LU do
   @moduledoc """
   Luxembourg IBAN parsing rules
+
+  ## Examples
+
+    iex> %IbanEx.Iban{country_code: "LU", check_digits: "28", bank_code: "001", branch_code: nil, national_check: nil, account_number: "9400644750000"}
+    iex> |> IbanEx.Country.LU.to_string()
+    "LU 28 001 9400644750000"
+
   """
 
   @size 20