Vatican IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "VA",
    ...>    check_digits: "59",
    ...>    bank_code: "001",
    ...>    branch_code: nil,
    ...>    national_check: nil,
    ...>    account_number: "123000012345678"
    ...>  }
    ...>  |> IbanEx.Country.VA.to_string()
    "VA 59 001 123000012345678"