A full exchange rate table (A, B or C) published by NBP.
:trading_date is only present for table C; tables A and B carry just
the :effective_date.
Summary
Types
@type t() :: %NbpReq.Table{ effective_date: Date.t(), no: String.t(), rates: [NbpReq.Rate.t()], table: String.t(), trading_date: Date.t() | nil }