Icons of Americana and modern keepers of the folk tradition, Gillian Welch & David Rawlings have shared “Empty Trainload of Sky,” a single from the forthcoming full-length, Woodland, the latest entry in the duo’s two-and-a-half-decade-spanning career. Recorded in Welch and Rawlings’ own Woodland Sounds Studio in Nashville, “Empty Trainload of Sky” features the duo’s trademark tight-and-somber vocal harmonies, lyrics evoking …