0.9.2  Added the function PyCalcValueXts() that has THREE (3) parameters: (i) symChr -
            a character vector of symbols; (ii) orderDfr - a data frame for "trades"; (iii)
            priceXts - a data frame (xts) for prices of symbols. It returns a "values" data
            frame (xts). Added an internal function PyDfrToXts() that converts a data frame
            with a date column (as the FIRST column) to an xts object. Modified output from
            a data frame to an xts object for functions PyBillOrderXts(), PyMarketSimXts().
            Modified input from a data frame to an xts object for function PyFileWriteCsv().