For lovers of theater, a St. Louis summer doesn’t truly start until Shakespeare is being performed. That moment comes next week, on May 31, as the St. Louis Shakespeare Festival opens its annual free performances in Forest Park. Tom Ridgley, the festival’s producing artistic director, breaks down this season’s unique take on “Twelfth Night,” set in Miami, and previews the other performances to come, including “The Merry Wives of Windsor” and an original production that combines Shakespeare and soccer.