registerRestInterface and registerWebInterface should return the router

[MartinNowak]

So that the functions become chainable just like get/post/any and such.

[s-ludwig]

Still not sure if method chaining is a good paradigm in D, considering the existence of with, but since we already have it in other places, I'd agree that it improves consistency. I'd just not want to advertise it as the standard way to access the API in the examples, maybe as a commented-out alternative right after the usual stand-alone UFCS call.

[MartinNowak]

updated

[s-ludwig]

Thanks!