Page "Plugins and extensions" not accessible

[janpapenbrock]

Visiting http://www.phpmetrics.org/documentation/plugins-extensions.html from the left hand menu gives a 404.

Might have been introduced by 97f8717 where the page name was changed, but no corresponding change in menu happened.

[Potherca]

The page is available at http://www.phpmetrics.org/documentation/plugins.html, the link in the menu is wrong. I have opened a pull-request to fix this.