Note that this is already done for wikis created by `auto-blog.setup`.
* [[tips/html5]] on by default (some day..)
* Remove support for old `.ikiwiki/comments_pending` from comment plugin.
+* Use yaml formatted setup files by default. (Not too compatability breaking
+ really.)
In general, we try to use [[ikiwiki-transition]] or forced rebuilds on
upgrade to deal with changes that break compatability. Some things that