Custom configuration

Hi

Firstly, thanks for the small and useful logging library.

I don't want to confront users with an `nlogger.json` file that requires knowledge of the module names. Also the current working directory isn't always the project root.

It would be super-cool if configuration could be set from the JS side, without the confusing message whenever `nlogger.json` cannot be found.

Thanks a lot,
Astro
