Now that the history question has been answered without so much as a spoiler alert, and now that Graham Linehan’s particular judgement has been pre-announced, let me urge you to read the book anyway. Tough Crowd is that rare thing, a memoir that will bear repeated readings. Yes, Linehan is just a really good writer, and yes, the book is a captivating blend of social and cultural history that doubles as a series of genuinely expert tutorials: how to write a joke; the golden rules of making a sit-com; casting for sit-coms; how to write a musical; how to keep a writing partnership together…