xts objects containing foreign exchange rates of
  Canadian Dollar (CAD_*), US Dollar (USD_*),
  British Pound (GBP_*), Euro (EUR_*), Swiss Francs
  (CHF_*), Japanese Yen (JPY_*), Chinese Yuan (CNY_*)
  with respect to USD (*_USD) and GBP (*_GBP) from
  2000-01-01 to 2015-12-31.