Support hierarchical .markdownlintignore files

[borekb]

This cli2 supports hierarchical config files (.markdownlint.json) but not ignore files (.markdownlintignore). This feels inconsistent, for example, I can customize lint rules per subfolder but can't customize ignore rules in the same way.

Why this is a problem in larger repos is described here: igorshubovych/markdownlint-cli#45 (comment).

[DavidAnson]

This is currently by explicit design - there's more discussion in #2. Specifically, all the globs need to be available before globbing starts for best performance. A single .markdownlintignore file in the current directory is easy to pre-read - but allowing multiple of them throughout the tree risks performance problems.

Aside: I may introduce "ignore" globs in .markdownlint-cli2.json for convenience, but those will explicitly be called out as a performance anti-pattern.

[borekb]

Thanks, the issue link should be #1 (this comment specifically) I believe.

[DavidAnson]

Yes, thanks for the correction! And there is an update there that's relevant here that may provide a nice resolution for both issues: #1 (comment)