Keep Variables same Across Builds

Happy to have a pull request

• Add more functionality
• Improve readability
• Kinder testing if a variable exists in a rule, great for people who don't use a css formatter
• Fix the current algorithm to use the old variables, its almost there

What's Changed

• [Snyk] Upgrade postcss from 8.4.21 to 8.4.24 by @navanshu in #40
• As always zero dependencies
• Keeping track of variables accross build by storing them in a file 💀

Full Changelog: v3.0.0...V4.0.0.0_Beta

Not available on NPM as it is actually broken, I don't want to break peoples working system only to get blamed for this