JSON-output

[theaino]

So apparently this issue for key-value-outputting (#271) exists for some time so I just went and implemented it.
It uses json because it is mostly used in such applications (rather than yaml or similar mentioned in the issue).

The output may look something like this:

$ ./headsetcontrol -jb?
{"device":"Logitech G533","battery":74,"capabilities":["sidetone","battery status","inactive time"]}

The system is made for allowing many changes in the future (other output values can be added in as little as one line).
For now, a success/error message directly in json is probably redundant because that is mostly managed by the return codes.

[Sapd]

Hey,
there is already a full implementation in the feature-output branch - including a full revamp (as discussed in the issue you linked): https://github.com/Sapd/HeadsetControl/tree/feature-output