Line annotation numbers <#>

Hi, please consider using unicode chars for this. Less likely to be confused as part of the text, and angle brackets can be dangerous if they make it to a shell somehow.

I notice the syntax highlighting is not completely working, and I think it is because of the angle brackets throwing things off.

e.g. ❶ ❷ ❸ ❹ ❺ ❻ ❼ ❽ ❾

Thanks for the cool book. I can help out with this, if you are interested.