Burundi IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "BI",
    ...>    check_digits: "42",
    ...>    bank_code: "10000",
    ...>    branch_code: "10001",
    ...>    account_number: "00003320451",
    ...>    national_check: "81"
    ...>  }
    ...>  |> IbanEx.Country.BI.to_string()
    "BI 42 10000 10001 00003320451 81"