Fix #1610 By exposing and documenting channel creation configuration

The use case right now, which won't be around forever, is that there's no way to swap Wreqr with Radio if you want. We put the set up of the channel in the constructor.

But this exposes the deeper problem...we should not be doing that stuff in the constructor. We should delegate that responsibility out to a method that handles that stuff, whether a user wants to override it or not.

So I'm not entirely sure what your argument is, but if it's that we should keep it in the constructor then I disagree. If it's the question of whether this is public or private...I'm thinking maybe private now, instead of public.