data-form: reformat <code> blocks so recent gtk-doc can cope
data-form: reformat <code> blocks so recent gtk-doc can cope

Recent (Markdown-based) gtk-doc doesn't like <code> spanning
more than one line, causing a build failure.

Reviewed-by: Guillaume Desmottes

freedesktop-unofficial-mirror/wocky,noonien-d/wocky,freedesktop-unofficial-mirror/wocky,freedesktop-unofficial-mirror/wocky,noonien-d/wocky,noonien-d/wocky