It's a good week for memoirs. The sixth and final installment of Maya Angelou's autobiography, A Song Flung Up to Heaven, finishes a bestselling trek the writer began more than 30 years ago with I Know Why the Caged Bird Sings. Random has done two printings for Song, for a total of 235,000. There was a groundswell of enthusiasm from booksellers before the book's April 2 publication, when Angelou was the cover story in both Ingram's Advance and Barnes & Noble's Community magazines. Also, O magazine ran an excerpt from the book in its April issue and the author appeared for the full hour on Oprah's show on April 4. Angelou is on a tour that includes Winston-Salem, N.C.; Atlanta, D.C.; New York; San Francisco; and Los Angeles.