Allowing a custom KarbonRoute to be used by applications with a custom starting path

For instance with these changes I can do the following:

```c#
            RouteTable.Routes.RemoveAt(0);
            RouteTable.Routes.Insert(0,
                new KarbonRoute(
                    "content/{*path}",
                    new RouteValueDictionary(new
                    {
                        controller = "Cms",
                        action = "Index"
                    }),
                    new MvcRouteHandler()));
```

And then I can have a Cms folder for my views rather than Karbon and also have my URLs starting with `/content/` allowing them to be out of the way of my application routes.

Doesn't look like there are any tests against KarbonRoute currently so I didn't put in a test, but happy to discuss ways of testing this.