add ability to whitelist selectors

[nellyk]

Currently we do not have an option to whitelist certain selectors if you do not want them removed by PurgeCSS using this library.
This feature would be to add support for whitelisting selectors.

PurgeCSS supports whitelisting https://purgecss.com/whitelisting.html.

Through these three options:

• Using specific selectors:
  whitelist: ['random', 'yep', 'button']
• Using a regular expression:

whitelistPatterns: [/red$/],
whitelistPatternsChildren: [/blue$/]

• In the CSS directly by adding this line to your css file.
  /* purgecss ignore */

[oneamexbot]

🎉 This issue has been resolved in version 2.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀