Add support for custom rules dirs

[apexskier]

Resolves #68

@markholland

[markholland]

If I set a Rules Directory in extension preferences everything works as expected but if I set the same directory in Project Settings instead then no linting appears to be happening.

I'm always using the browse button when adding a Rules Directory.

Edit: If I add an absolute path to Project Settings it works. Using browse from Project Settings as I'd expect it adds a relative path but that appears to lead to no linting. The relative project path is .eslint/rules if this helps to know.

[apexskier]

Very weird - this is the underlying bug for the issue you found - gkz/optionator#34

[apexskier]

@markholland Can you test once more? I added a workaround for the underlying issue. After digging around in the dependencies eslint uses for options parsing, I don't expect a root cause fix to come any time soon, but this should work.

[markholland]

Yes, this is now working with relative paths in Project Settings.

[github-actions]

Included in release v1.7.0