allow specifying a url name as the "from path" on a route

This allows you to pre-define a named url using `url` and then use
that url in a later route.  There is no difference using this approach
vs. supplying a url name at route-time.  It is purely organizational
or preferential sugar for defining routes.

@jcredding ready for review.  I'm curious if pre-defining urls will make the routes file easier to read on large routes files?  Thoughts?