Feature Request: --fail-if-warnings

[cleborys]

Pandoc supports the --fail-if-warnings option to exit with an error code if any warnings were generated.
This does not seem to cover warnings generated by pandoc-fignos, for example in case of bad references.

It would be nice if pandoc-fignos supported this option too, preferably by gaining access to the options passed to pandoc itself, or otherwise through its own configuration option.