Add option to disable printing errors to standard output

[Nyholm]

This is technically a BC break, but since it is an internal tool ¯\(ツ)/¯

Symfony-docs shows the errors:

https://github.com/symfony/symfony-docs/blob/5.x/.github/workflows/ci.yaml#L76-L78

[wouterj]

Hm.. But we build the -vvv argument. So I dont think it should be related to verbosity.

I'm almost 100% sure that I added -vvv as a desperate move to try to get error output (I added the CI pipeline with 0 config of this tool). I wouldn't give any weight to the docs CI pipeline in any decision about this tool.

That is true, but is that important?

Not really, but it's a good reference (it's the most commonly used documentation build tool, so if it does something, someone probably thought about it and wanted that feature). I think it makes sense to always show errors.

[Nyholm]

I've updated the PR. It will now just add an option to disable parsing errors on std-out.