I do like the idea of using GitHub's wiki if there's a way to export the data and back it up. It saves us the trouble of maintaining a server, and we really don't need fancy features anyway. It would be ideal if we could also import our existing wiki content, but perhaps Tomasu could export it and we could script it up? If I'm not mistaken, isn't GitHub's wiki accessible through Git? Or am I thinking of some other platform?
Sounds good to me. The only hitch with trying to import existing Wiki articles is probably that links and things won't match 1:1. We can always do our best to automate repairs and then leave future repairs as an exercise to the reader.
There may be a hitch. I cannot seem to clone liballeg/allegro5.wiki.git. It seems the permissions for that are still locked down to contributors, so you'd probably have to clone the repo into your own account, then make changes to the wiki, then submit a pull request? I'm not sure. It's something we need to answer first.