As discussed in mastodon#764 there are quite a lot of outdated links in the
mastodon documentation. In basically all cases this was resolved by
simply wrapping the old plain markdown link in hugos `relref`
function[^0].

While quite a lot of links on the `/zh-cn/` also appear to be broken,
these can not be fixed by just wrapping them in `relref`[^0]. Those are
all links to `/spec/` subpages which are just not translated to `/zh-cn/`
version. Therefore, `/zh-cn/spec/` has been excluded from the automated
checking as described in the next section.

The page has been checked using the linkchecker[^1] utility. One process
is running `hugo serve` in order to see all changes in real time and
notice errors directly in your browser. In a separate command prompt the
command `linkchecker http:https://localhost:1313 --ignore-url=/zh-cn/spec` is
being fired up. Note the `--ignore-url=/zh-cn/spe` to exclude the just
not existing parts of the page as mentioned in the previous paragraph.

There still is some ToDo on the table since quite a lot of the anchors
appear to not be set or at least differ from previous versions. One
example: on `/client/authorized/` is a link to
`/client/token/#creating-our-application` while the id of referenced
heading is `app`. These changes **do not** fix those Issues as it would
require way more time.

[^0]: https://gohugo.io/functions/relref/
[^1]: https://github.com/linkchecker/linkchecker

Close mastodon#764