Add ignore file(s) support

[AndersMad]

Let's you ignore SCSS file(s):

Change in index.js

const sassFiles = glob.sync(path.join(dir, '**/*.scss'), { ignore: opt.ignoreFiles });

Usage:

const unused = fusv.find("./scss", { ignoreFiles: ["**/_crappy-vars.scss"], ignore: ["$crappy-var"] });`

[Dervisevic]

+1 would love to have this feature as well. We have a style-dictionary generated file that has a lot of unused variables and would be great to be able to ignore it and not have it sit elsewhere to avoid getting scanned.

[XhmikosR]

Happy to accept a clean PR with tests :)