Serbia IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "RS",
    ...>    check_digits: "35",
    ...>    bank_code: "260",
    ...>    branch_code: nil,
    ...>    national_check: "79",
    ...>    account_number: "0056010016113"
    ...>  }
    ...>  |> IbanEx.Country.RS.to_string()
    "RS 35 260 0056010016113 79"