Verified support for PHP 8.3

Updates the documentation to reflect additional PHP version support, including PHP 8.3.

Fix deprecation warnings for PHP 8.2

• Migrated test suite to GitHub Actions
• Addressed Dynamic Property deprecation warnings for PHP 8.2
• Updated typo in composer.json's provide statement

Drop unsupported PHP and PHPUnit versions

• Dropped support for PHP 7.2. This version lacks security updates since late 2020.
• Dropped support for PHPUnit 7. This version lacks security updates since early 2020.

While the package currently allows PHP 7.3, it's strongly recommended you upgrade to PHP 7.4 or 8.x as soon as possible.

Add PHP 7.4 & 8.0 Support

• Add support for PHP 7.4
• Add support for PHP 8.0

PHPUnit 8 & PHP 7.3 support

• Support PHP 7.3
• Support PHPUnit 8
• Drop testing support for PHP 7.0 and PHPUnit 6

Initial release

This release provides a working instance of OAuth and OAuthException ready for use.