Addition of an --ignore-errors flag

[mortonmills]

I've been using pandoc to convert repo docs (markdown, pandoc, node, vscode.... ) into html and epubs for offline use.
However, I receive errors in some cases and only receive partial output.

I've searched the pandoc issues and discussions,
#4893 requested this as an option several years ago.

I realize the current solution is to use filters.
However, having an --ignore-errors flag would greatly simplify usage when errors are acceptable
and could also act as a last resort option in the case filters won't do or are too complex to write.

[tarleb]

In general, errors are throws if there is no reasonable way to continue with the execution. Specific cases where a warning might suffice should be looked at individually.