Thanks for the pointer. This is useful and interesting, but I wasn't clear enough - I need the audio on my mobile phone and it needs to bookmark where I left off, like audio book players and podcast apps do. Pocket has a very nice workflow for this because I can bookmark a web site in Firefox, then play back on mobile later. I've also used
http://talkify.net and saved the whole .mp3 file as an audio book to my mobile device, but talkify and Pocket only work with HTML accessible over http via a public URL. But thanks, and I'll probably learn something from this tool as well.
Besides - another reason why it would be cool if
http://books.pharo.org had supplementary HTML builds with unique anchors for chapters and sections because this makes it very easy to point to specific sections in the books when answering questions on the mailing list.