Related to #2524 and #3171, this is a long lingering thought that apparently was not recorded in the issue tracker: add an option to upsc (or an alternate client?) to display device(s') information as a JSON structure. Depending on tools that upsc output is piped into, JSON nowadays might be friendlier than a key-value list of the (g)olden days.

Loosely also related to #1306 (might as well "dump data" in JSON optionally... maybe add that as a NUT protocol command/option?) and #3138 (add a sub-object with schema for the data points shown).

Part of this quest is converting JSON methods originally added in #3171 into share-able common code that different clients (maybe even server) can use to emit consistently structured documents.