Add PHP 8 support

What's Changed

• Add PHP 8.0 support by @soukicz in #3

New Contributors

• @soukicz made their first contribution in #3

Full Changelog: 2.0.0...2.1.0

Upgrade package

• Clean up gitignore
• Upgrade PHPUnit
• Add psalm as static analyzer
• Refactor validator
• Remove composer.lock from package
• Update README.md
• Update dependencies and add script
• Add github actions
• Add github templates

XML Validator

1.0.0

Initial commit