For more than 30 years, Jane and Michael Stern have traversed the country in search of the best in regional American cuisine. They coined the term “roadfood,” which became the name of their encyclopedic book and Web site. The ninth edition of “Roadfood: The Coast-to-Coast Guide to 900 of the Best Barbecue Joints, Lobster Shacks, Ice Cream Parlors, Highway Diners, and Much, Much More” came out this year.