post process or ignores before diff

[yasirroni]

Hi, I'm a contributor of nb-clean. I use that to clean execution count and metadata of notebook before push any commit. Do you accept any contribution around skipping execution count and metadata diff? I think it haven't been implemented by you.

I think there are two possibilities.

1. Do a post process that run git filter on the notebook before it is cleaned.
2. Parameters to clean diff based on the given argument

Option 2 is better I think. Since nbdime support ignores

Then, the question is, does this package respect nbdime config nbdime_config.json?

[yasirroni]

After some testing, it seems that pytest-notebook ignores nbdime_config.json, both on the pytest target folder and on root folder.