Feature/forward article id to modules

I want to implement a module that allowes the user to attach files to articles. But the corresponding hooked functions (for example modulename_article_start and article_end are not able to know in which article they are in. So this is a suggestions to allow to pass more information to the functions (optionally).

It works like this: whenever hook is called, you can pass an associative array as second argument. Whenever one of the keys of this array matches the name of an argument of a hooked function, it is passed as this argument.

So this pull request should not break BC and enables modules to do more stuff.