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"
    ...>  }
    ...>  |> IbanEx.Country.LU.to_string()
    "LU 28 001 9400644750000"