This allows the CLI to expose options that the renderers can offer.
These options are limited (string, int, bool and bytes), so no lists
or choices, etc.
Each renderer's options are also global options, meaning they're always
present (although grouped). There's two ways of handling this:
a) Prefix each option with the renderer's name, duplicate options are
unique
b) Deduplicate options with duplicate names and prefix 'renderer'
The current choice is a) because b) might confuse people that an option
which only applied to one renderer would be available for all, but
comes with the inconvenience that users must adapt the option name for
those that are duplicated with the same meaning.
This is at least functional and extendable in the future but still a bit
clunky. We could have brought the entire configuration mechanism into
play, but each renderer would require a context and a config_path and
so on, meaning massive overkill and a non-addition-only API change.
Mike Auty