Belgium IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "BE",
    ...>    check_digits: "68",
    ...>    bank_code: "539",
    ...>    branch_code: nil,
    ...>    national_check: "34",
    ...>    account_number: "0075470"
    ...>  }
    ...>  |> IbanEx.Country.BE.to_string()
    "BE 68 539 0075470 34"