I use perldoc / POD to write man pages and that works well. It's simple to write and there are tools to convert it straight to man pages, text or HTML.
For example: https://raw.githubusercontent.com/libguestfs/libguestfs/mast... and the output as HTML: http://libguestfs.org/virt-p2v.1.html
(The output in 'man' looks really good too, but I don't have an easy way to demonstrate that.)