Better support packages which have complex doc setup

[fingolfin]

Right now the code for copying the documentation to the website is very simple minded. But @schnellecom is working on a package which has things in subdirectories of the doc directory, and this confuses our code updating the website. Also some packages may have more than one manual they wish to publish on the website, etc.

To support this and other situations I am not even aware of yet, we need a new mechanism.

Idea 1: add a hook script similar to the .release script, say .publish, which is given the path to the package, plus the path to the website directory, and then is supposed to copy stuff. This is very flexible but of course also has a danger of screwing it up.

Idea 2: we allow for an optional text file which is just a list of files or directories to publish (maybe allowing for simple globs), and then we take care of copying them.