ikiwiki/ tips/ switching to usedirs

As of version 2.0, ikiwiki will switch to enabling the 'usedirs' setting by default. This will break all URLs to wikis that did not have 'usedirs' turned on before. You can either follow this procedure to convert your wiki to usedirs, or edit your setup file and turn usedirs back off.

- Upgrade ikiwiki to 2.0.
- Force ikiwiki to rebuild your wiki, by using `ikiwiki-mass-rebuild`, or manually.
- Since usedirs is enabled, ikiwiki will have created a bunch of new html files. Where before ikiwiki generated a `dest/foo.html`, now it will generate `dest/foo/index.html`. The old html files will be removed.
- If you have a blog that is aggregated on a Planet or similar, all the items in the RSS or atom feed will seem like new posts, since their URLs have changed. See howto avoid flooding aggregators for a workaround.
- Now all the URLs to pages in your wiki have changed. See redirections for usedirs for instructions on setting up redirections to keep the old URLs working.

## Why usedirs?

There are several advantages to `usedirs`, including simpler URLs, URLs that aren't dependent on the underlying implementation (`.html`), and being able to use URLs as tags as described in the rel-tag microformat.

The main disadvantage is that it is harder to browse using `file://` URIs, since `file:///dir/` doesn't automatically translate to `dir/index.html`. This is something one could fix in the browser though.