I have tried to follow Hugo's development but lost track with its constant evolution and addition of features I do not need...therefore for now I follow a simpler path: I keep my data in markdown files and I plan to switch to asciidoctor for good; it's quite old, it's battle-tested, and offers me many options to produce various forms of output; be it HTML, PDF, ePub, etc...

If O'Reilly trusts it to produce its ebooks, then I'm sure it worthy of my time and effort!