Add Credo configuration and Dialyzer ignore file

- Introduced a new Credo configuration file for code quality checks. - Added a Dialyzer ignore file to suppress known
warnings. - Removed TODO comments for Bulgarian and Icelandic IBANs. - Updated the Dialyzer configuration in mix.exs to
include

lib/iban_ex/country/bg.ex

@@ -1,6 +1,4 @@
 defmodule IbanEx.Country.BG do
-  # TODO Bulgaria IBAN contains account type (first 2 digits of account number)
-
   @moduledoc """
   Bulgaria IBAN parsing rules
 

lib/iban_ex/country/is.ex

@@ -1,6 +1,4 @@
 defmodule IbanEx.Country.IS do
-  # TODO Iceland IBAN contains identification number (last 10 digits of account number)
-
   @moduledoc """
   Island IBAN parsing rules