Beautiful, melancholy and intellectually stimulating, “Dahomey” is a documentary that should be seen by all.Some films shine brighter than others. RaMell Ross’ “Nickel Boys,” a stirring cinematic adaptation of Colson Whitehead’s Pulitzer Prize-winning novel, is polished to a remarkable luster. Its assuredness comes on like a stiff breeze on a sticky Southern summer day, telling a boldly conceived story of two Black kids named Elwood and Turner, living during the height of segregation in Florida.