apropos(1) is a last summer's Google Summer Of Code project implemented in NetBSD. It allows a relevance-based search through manpages written in mdoc.
As maybe Markdown is going to be in the source tree, we want to extend apropos to also be able to search through generic documentation articles.

Your task would be to research the possibility of creating another binary that is able to search through markdown documentation pages, creating its own index file (mandb).
If you are having fun with this, thinking about ways how to combine the two binaries into one single documentation search binary would be good.
Mail announcement import of apropos: http://mail-index.netbsd.org/tech-userlevel/2012/02/01/msg006040.html