Add option to disable creation of mermaid-filter.err

[CmdrSharp]

Currently, mermaid-filter fails on read-only filesystems (which is not uncommon in Docker, for example).
This log file should, I feel, be optional. Along with that, perhaps an argument to specify a path for it would be good?

[chasecaleb]

It would be particularly nice to avoid creating this file when there aren't any errors.

[raghur]

Can you pls try this branch out? tq

[chasecaleb]

@raghur Hi, so sorry I just realized you're probably waiting for a response from me. Unfortunately I don't have a straightforward way to test out a branch that isn't published on NPM. When you merge and publish NPM then I'm happy to try it out, though.

I skimmed the PR and it looks sane to me, if that's any help. Sorry about that.

[ghosty141]

I'd prefer a mode that just doesn't write any files at all.