Greece IBAN parsing rules

Examples

    iex>  %IbanEx.Iban{
    ...>    country_code: "GR",
    ...>    check_digits: "16",
    ...>    bank_code: "011",
    ...>    branch_code: "0125",
    ...>    national_check: nil,
    ...>    account_number: "0000000012300695"
    ...>  }
    ...>  |> IbanEx.Country.GR.to_string()
    "GR 16 011 0125 0000000012300695"