code: public static BtcFormat getInstance(int scale, int minDecimals, int... groups) {
          return getInstance(scale, defaultLocale(), minDecimals, boxAsList(groups));
      }
docs: Return a new fixed-denomination formatter with the specified fractional decimal
  placing.  The first argument specifies the denomination as the size of the
  shift from coin-denomination in increasingly-precise decimal places.  The returned object will format
  and parse values according to the default locale, and will format the fractional part of
  numbers 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.