This year has been great for stocks, as indexes confirmed the presence of a bull market and then went on to reach multiple record highs. The Dow Jones Industrial Average, which includes 30 of the top large-cap stocks powering today's economy, roared past 40,000 for the first time ever and is now heading for a gain of about 16% since the start of the year.The great news is that this positive momentum may be far from over. History shows that bull markets generally last much longer than bear markets -- nearly ...