Photo: Valerie Terranova At Playwrights Horizons, each slim program comes stuffed with a copy of the theater’s in-house literary magazine, a collection of supplemental essays, interviews, and “playwright’s perspective”s called Almanac . Read one front to back and you get a Thanksgiving dinner’s worth of context, along with a real sense of just how much talking and thinking and self-questioning and self-justifying goes into making any given play. Take No Singing in the Navy , Milo Cramer’s semi-