editorconfig support

[Kernald]

A bit of context in DavidAnson/markdownlint#303 - it would be great to read configuration from a .editorconfig file. A few interesting properties would be the max line length and the type of indentation for example. Other tools for other languages (e.g. ktlint for Kotlin) support this, and while the initial issue mentions VSCode being a better place for this than here, I think there's some value in having a single source of truth for the configuration whether you're running in a IDE or in CI.

[piranna]

I think a better place would be https://github.com/DavidAnson/markdownlint-cli2, vscode already has plugins for editorconfig, so it makes total sense to use an .editorconfig file values if they are available. Not sure if natively or with a plugins system.

[piranna]

I've open an issue for markdownlint-cli2 at DavidAnson/markdownlint-cli2#179