code: public static BtcFormat getCoinInstance(Locale locale, int scale, int... groups) {
          return getInstance(COIN_SCALE, locale, scale, boxAsList(groups));
      }
docs: Return a newly-constructed instance for the given locale that will format
  values in terms of bitcoins, with the given minimum number of fractional
  decimal places.  Optionally, repeating integer arguments can be passed, each
  indicating the size of an additional group of fractional decimal places to be
  used as necessary to avoid rounding, to a limiting precision of satoshis.