[racket] Hierarchical loggers

> The `configure-runtime` submodule name is special: when "main.rkt" is
> run as a program, then `configure-runtime` is loaded and instantiated
> first --- before the result of "main.rkt", and before the imported
> "foo.rkt" and "bar.rkt" modules.
>
> This strategy only makes sense for configuration that is especially
> main-like, though. It doesn't compose for larger things that are built
> on "main.rkt".

Also keep in mind that `configure-runtime` isn't called by `enter!`[1].

You use `enter!` (directly or indirectly) in some interactive
development systems such as XREPL or Geiser.

However this is N/A in DrRacket and with `racket your-program.rkt` --
in those cases `configure-runtime` will be called.

[1]: http://www.mail-archive.com/users%40racket-lang.org/msg22112.html