def format(number)
      case number
      when Float then format_float(number)
      when Integer then format_integer(number)
      else fail ArgumentError
      end
    end
def format(number)
      case number
      when Float then format_float(number)
      when Integer then format_integer(number)
      else fail ArgumentError
      end
    end
Initialize a formatter with the desired options.

 @param [Hash] options the options to create a formatter with
 @option options [Integer] :decimals (2) Number of decimal places
 @option options [Boolean] :fixed (false) Fixed decimal places
 @option options [String] :separator ('.') Decimal mark
 @option options [Integer] :grouping (3) Number of digits per group
 @option options [String] :delimiter (',') Delimiter between groups