typos + consistency

Fixed some typos, and made the starting numbers of the Fibonacci sequence consistent between examples (both "0, 1,..." and "1, 1,..." seem correct, but seeing them mixed was confusing to me on first reading).

Please review if that is correct and I didn't change the meaning in some bad way.

Also, I'd like to take this opportunity to thank you very much for this ***A M A Z I N G*** guide. I really, really admire it in various aspects. And it read as a novel to me, without fumbling nearly all way through. Also a valuable example of lifetimes usage. And it's great that you show some errors and how to resolve them; that's one of the highlights of this guide, and I think I've never seen errors used so well as an educative means yet.

So, thanks again.