Consistent output formatting

[s-hamann]

The output of the various subcommands is somewhat inconsistent. For newly generated tokens just the secret value is printed, domains get printed as one name per line, records are in zone file format and the rest is mostly unchanged JSON as returned by the API. This works all right for human processing, but may impose difficulties for automated processing.

I'd be nice to have a global --format option to choose between JSON, something easily greppable and something that is more human-friendly than JSON (and might be condensed to only the most commonly useful information).