Move away from DocBook for documentation

[rdmark]

The DocBook toolchain relies on XML parsing and XSL stylesheets that is heavy, complex, and partially on the verge of obsolescence.

For one, we use traditional non-namespaced DocBook XSL style sheets which are two generations behind where DocBook is today. The docbook-xsl package is orphaned in Debian, for instance.

Another concrete drawback is that Debian tries to proactively strip XML related dependencies from architecture dependent builds, to save on computing resources and speed up builds. But this can’t be done for netatalk because of how we generate the troff man pages from XML.

This is to look into converting the documentation sources to a markup format that is parseable by pandoc, such as Commonmark. This would allow us to transcode to human readable formats with the light-weight cmark.