When times get tough, it’s time to hit the books. And a number of county residents have done just that, making a monthly book swap an increasingly popular event. The fourth anniversary of the Nevada County book swap will take place Sunday in the back warehouse of Scooter’s Place at 139 Joerschke Drive in Grass Valley. The event takes place the first Sunday of the month, even during the holidays, and offers a platform for people to bring in books, magazines, CDs and DVDs and take away materials of interest as well. Originally, the swap was an idea founder Cheryl …