Chicago-based soul singer Willis Earl Beal once told an interviewer he wanted to be an underground cult legend, which isn’t a thing people usually set out to become on purpose. Beal, 28, recently issued his official debut, “Acousmatic Sorcery,” a roughly hewn, bewitching, cult-stardom-baiting collection of anti-folk and blues songs. It positions Beal as the heir to outsider artists such as Daniel Johnston and Wesley Willis, with a back story to match: Formerly homeless, Beal used to write songs, record them to burnable CDs and leave them in public places to be found.