def open_binary filename, extension=nil, options={}
      extension = file_extension(filename) unless extension
      f = open(filename)
      send("load_#{extension}".to_sym, f, options)
    end
def open_binary filename, extension=nil, options={}
      extension = file_extension(filename) unless extension
      f = open(filename)
      send("load_#{extension}".to_sym, f, options)
    end
Open the file in binary, read-only mode, do not read it, but pas it throug to the extension determined loaded

 @param [String] filename a string with a reference to the file to be opened
 @param [String] extension an optional string enforcing a certain parser (based on the file extension, e.g. 'txt', 'csv' or 'xls')
 @return [Workbook::Book] A new instance, based on the filename