In 18.104.22.168 we did change the way routes are registered as we added support also for web api routes and wanted to have a consistent way to register routes. We dropped routing from our .NET 4 build because we use new .NET 4.5 classes for routing and web api.
To plugin custom routes now you implement this IRegisterRoute interface which has methods for mvc routes, api routes and filters to be registered, you can just do nothing in the methods that aren't of interest.
An example implementation is in the mojoPortal.Features project where we add an api route for forum notification moderation.
whatever class/type/namespace where you implement the interface, you plug that in by adding a config file under /Setup/RouteRegistrars that declares the type.
Then the methods on your RouteRegistrar will be called during application start.
Sorry for the breaking change, I didn't think many people were using the routing feature. It is pretty straightforward to implement the new way. If you have any trouble making the needed changes let me know and I'll try to help.