Remove implicit folder structure from config

Remove the need for an implicit config folder structure (which is badly documented, in the original Wraith Ruby project as well).

Now you pass a full relative path e.g. `./config/my_config.json` or `./my/other/folder/my_config.json`. Which allows for much saner configuration of projects, meaning users don't have to create arbitrary directories for just a wraith config file or messing with their nicely organised existing config directories by putting a json file at the top level.

I realise this is a divergence from the 'upstream' Wriath config, but in this case I think it's an improvement!