Diesel: make ->- as more generic var-args method.

Now instead of:

URI("....")
      -- foaf.knows ->-  graphA
      -- foaf.knows ->-  graphB
      -- foaf.knows ->-  graphC

it is possible to write:

URI("....")
      -- foaf.knows ->-  (graphs: _*)

I found it very convenient, a lot of time i have a list of graphs that I need to connect to some node using same predicate so I need to write manually  something like:

pgs foldLeft(graph)((acc, g) => acc -- predicate ->- g )