Return with a non-zero exit code on failure

[greg0ire]

It would be great to have aglio return something else than zero on failure (or is it warning ?), to be able to use that in CI, for instance. Maybe introduce a --strict option for that?

[greg0ire]

My workaround for the moment : test $(aglio --input /docs/ws.apib --output ws.html 2>&1 >/dev/null |wc -m) -eq 0 (thanks @L-P )