Added more examples, and added more charts to illustrate what
I was talking about. Notably, added error bars to the weight
readings to make the possible range of values clear.
I got the original code from the author, Cameron Davidson-Pilon,
modified it for the minor changes I make for the book, and put it
in 538.json. The main gain is that somebody doesn't need bleeding
edge matplotlib installed to get the 538 look.
