The October 2015 edition is now available for free download.
See:
http://neilkolban.com/tech/esp8266/
This release sees revision bars (I hope) on the document which are the delta changes since September. I took 2 weeks vacation in September (not computing or electronics of any kind) and also have been heavy into the JavaScript engine port for Espruino ... as such, book maintenance took a back seat. However, I like to make sure that I keep diligent and the 1st of the month is new publish day ... even if only a few pages have been updated.
Hoping you will enjoy ... as always comments welcome and tons more content to come in the many months ahead.
Neil