HSEARCH-1471

I think this is ready to go. There might be still minor edges, but we need a full docs review prior release anyways (some sections are out of date, for example Services).

The asciidoctor html output is not part of the main build. To build the docbook source and then run the docbook plugin is part of a profile now (enable via _-Drelease_). 

Let's switch to Asciidoc and take it from there.