Allow value only responses via API with ?raw

[tmaiaroto]

It would be convenient if the API returned just the key value when ?raw querystring was added to the URL. This would be very convenient for binary data if the Content-Type could be figured out...But for the time being this might make it more convenient to work with discfg within an application.

For example, what if someone didn't want to use JSON? Now the response could be plain text parsed in whichever way necessary. Maybe it's YAML or TOML, etc.