“Visionary” is a term that has become somewhat overused in the outsider art field — and over on the contemporary-art side of the broader art market, too. In some ways, “visionary,” which is properly used to describe distinct or novel worldviews, as well as the sometimes bizarre imaginings of both self-taught and academically trained artists, has become, thanks to hyperbole-spewing publicists and dealers, as meaningless as “amazing,” “epic,” or “awesome” — a mere banality assigned to everything from bad pop songs to hamburgers. The current exhibition The Life and Death of Charles Williams, however, illuminates an unusual and varied body of work that is nothing if not genuinely, emblematically visionary.