For the first three of its four-year history, Vacaville’s Medieval Fantasy Festival arrived with mostly earnest and serious-minded matters and pursuits. They included guest lecturers and experts on fantasy, especially the kind imagined by British author J.R.R. Tolkien, who wrote the “Lord of the Rings” trilogy and serves as the festival’s spiritual godfather. And the two-day event’s themes center around the sober ideas of friendship, community and environmental stewardship, that is, being “green.” Medieval fling