All of a sudden, two new bookstores have popped up at Rockville Town Square. The Story House, a mobile store for kids, has taken over a corner of Dawson’s Market with a charming and well-curated selection of recent titles. And just a block away, between Lebanese Taverna and Bonchon, local nonprofit Turning the Page has opened a popup shop to benefit its literacy efforts in D.C. The store, called Carpe Librum, will be open through August selling used books, CDs and DVDs.