Add multi-segment matching to router

[jgaskins]

Right now, the router cannot match on a path segment that contains a /. For example, neither of these routes can currently be matched:

  route 'foo/bar' => FooBar.new
  route 'foo/:foo_id' => FooDetail.new

If we, instead of splitting the URL path on /, match whatever comes at the beginning of it (removing the matched part to pass to subordinate routes), we would be able to handle these cases.