developer/api-usage: appendix A done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
developer/ui-plugin: make this appendix as XXX

There is no EayunOS support UI plugin at the moment.

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
developer/certificates: appendix C done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
developer/enumerated-value-translation: appendix D done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
developer/event-codes: appendix E done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>
developer/timezones: appendix F done

Signed-off-by: May <sirhuntthepure@users.noreply.github.com>