In the last weeks, I revised chapters 1 to 7, and moved the online version of the book to a dedicated website. This should make it easier to find the book.
The most changes got chapter 6 discussing memory management. The previous version was already quite good, but it was obvious that there was room for improvements. So I drastically rearranged the content, and added as motivation the suggested "iterator invalidation", and the enum example from the 2015 blog post. The other six chapters have not changed that much. I think chapters 8 to 25 are already quite good, but I will try to revise them as well this year. For macros and async we have still no final decision -- should be a lot of work to create that chapters.