||Function is called after the plugins have been loaded. If the string placeholder
in the example URL http://www.domain.de/placeholder is
a defined short URL, the user is redirected to the correct URL.
||Function is called after an article has been saved. Checks whether a short URL
has been given via $_POST and saves/deletes it.
||Constructs the HTML code containing table rows which are added to the end of the
article edit form
||Computes an error message which describes the given error code.