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.
Merge pull request #92 from redding/kr-addurl-redir-route

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