The Avett Brothers are coming to town again, country star Vince Gill is making his Savannah debut and plenty of genre-spanning musical staples and newcomers are on the lineup of next spring’s 2014 Savannah Music Festival.Organizers will unveil the full schedule for the March 20 - April 5 festival’s sound-packed 17 days at a free concert tonight featuring mandolinist Sierra Hull, set to perform again during the festival with the legendary Ricky Skaggs.Tennessee native Hull, 22, and her bluegrass band, Highway 111, are set to take the stage at the Charles H.