To the surprise of many of its patrons, the Gleason Public Library in Carlisle made an institutional decision to stop charging overdue fines five months ago. And it isn’t the only one - libraries in Dover, Littleton, Chelmsford, and Westford have made similar changes recently, though many libraries in communities west of Boston are staying with the traditional system of collecting small amounts for books and larger fees for DVDs that are returned late. According to Gleason Public Library director Angela Mollet, the change fits in with her philosophical outlook that there should be no obstacles to reading.