Two other tools that render images from ascii are ditaa (http://ditaa.sourceforge.net/) and plantuml (http://plantuml.com/). Those tools, some scripts to render and combine markdown and images, and DrawIt (+ some other vim tools like 'boxes' (not sure if that still has a web page), 'sketch.vim' and 'boxdraw') make for the least painful, versionable documentation system, for me. ('least painful' in the sense that I still need to code way too much to get it all to work, but there isn't anything ready-made and stable enough that I have been able to find the last decade).