def initialize(ref, range, sheet, options={})
      @ref = ref
      self.range = range
      @sheet = sheet
      @sheet.workbook.pivot_tables << self
      @name = "PivotTable#{index+1}"
      @data_sheet = nil
      @rows = []
      @columns = []
      @data = []
      @pages = []
      @subtotal = nil
      @no_subtotals_on_headers = []
      @style_info = {}
      parse_options options
      yield self if block_given?
    end
Creates a new PivotTable object
@param [String] ref The reference to where the pivot table lives like 'G4:L17'.
@param [String] range The reference to the pivot table data like 'A1:D31'.
@param [Worksheet] sheet The sheet containing the table data.
@option options [Cell, String] name
@option options [TableStyle] style