This turned out to be a bad idea. The thing is that some resources need
to be referred to in multiple ways -- for example, different texts in
links of different kinds, or using the URL directly in some cases. The
existence of `get-resource-path' is a witness for this problem, since it
was used for such cases -- this function is removed as well.
There's no point in trying to generalize this here: instead, go back to
a simpler system where a resource always returns its URL (with an
optional argument to get an absolute URL). When a `referrer'
functionality is needed, build it on top of that, in a place where it
makes more sense. (That is, in a specific code for generating content,
where there could be a decision that resources have plain links and also
a very short link for use in navbars.) Otherwise, it's usually simpler
to just define resources and referrers separately (as different
bindings, the latter uses the former).
