Link type

This is pretty minimal, but I think it handles the use case here: http://wagn.org/inclusions_to_define_link_targets

I think the view solution is preferable here.  One criteria I want to consider in pondering any additions to syntax is how/whether they would complicate the inclusion editor (coming soon).  I think that's going to be a fairly tractable task because  of how hard we've worked to keep inclusion syntax simple.