Also: Rock the Park in Kennett this weekend By Denny Dyroff, Staff Writer, The Times For almost four decades, the Chester County Restaurant Festival (Gay Street and downtown area, West Chester, 610-436-9010, http://chestercountyrestaurantfestival.com) has been treating visitors to the borough with the opportunity to sample a wide variety of gourmet treats. This year, the free festival, which will...