code: def method_missing(name, *args, &block)
        super unless operands.keys.index(name.to_s)
        operands[name.to_s]
      end
docs: A spread sheet builder is doing arithmetic operations and can be called
   like this:
  
       SpreadSheetBuilder.new(outfile:   "out.csv",
                              files:     "f1.csv,f2.csv",
                              r:         "true,false",
                              c:         "false,true",
                              aliases:   "a,b",
                              operation: "(a*b).transpose",
                              ds:        ",",
                              equalize:  "true",
                              print:     "true").execute
  
   outfile::   file where the result of the operation is written to
   files::     files that hold the spread sheet data
   r::         indication whether the corresponding file has row labels
   c::         indication whether the corresponding file has column labels
   aliases::   symbols that correspond to the spread sheet created from the
               files. The symbols are used in the operation. The symbols have
               to be choosen carefully not to conflict with existing methods
               and variables
   ds::        decimal spearator '.' or ',' where '.' is default
   equalize::  indicates whether different column sizes should be equalized
   operation:: arithmetic operation on spread sheets using the aliases as
               place holders for the spread sheets. The last evaluated
               operation is returned as result and saved to outfile in case
               the result is a spread sheet. In all other cases the result
               can be printed with the print flag.
   print::     print the result
   Returns the spread sheet operands when called in the arithmetic operation