Add baseline support

[dallasgutauckis]

Resolves #167

[rs-georg]

Would be great if this PR could be merged and released.
Not having baseline support is keeping us from using this plugin. We want to migrate from https://github.com/JLLeitschuh/ktlint-gradle. However, we have existing baseline files that we cannot drop since fixing all the issues would create an unacceptable effort.

[ThomasRichtsfeld]

We are also currently integrating this plugin but need baseline support as formatKotlin doesn't resolve all the issues.
Any help needed

[jeremymailen]

Closing for now since it's out of date. We can recreate if we plan to add baseline support.