Added a config to directly use top level keys as parameters

My usecase is the following: Some of apps I'm working on are using YAML file to store config without having a single top-level keys (like `parameters` or `config`). And I would be happy to be able to use this handy scripts (without the need to change the way we are structuring our config file).

I don't know, maybe this is a bit too far away of the original idea of this library...