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

lib/iban_ex/country/bg.ex

@@ -1,6 +1,13 @@
 defmodule IbanEx.Country.BG do
   @moduledoc """
   Bulgaria IBAN parsing rules
+
+  ## Examples
+
+    iex> %IbanEx.Iban{country_code: "BG", check_digits: "80", bank_code: "BNBG", branch_code: "9661", national_check: nil, account_number: "1020345678"}
+    iex> |> IbanEx.Country.BG.to_string()
+    "BG 80 BNBG 9661 1020345678"
+
   """
 
   @size 22