Finland IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "FI",
    ...>    check_digits: "21",
    ...>    bank_code: "123456",
    ...>    branch_code: nil,
    ...>    national_check: "5",
    ...>    account_number: "0000078"
    ...>  }
    ...>  |> IbanEx.Country.FI.to_string()
    "FI 21 123456 0000078 5"