Merge pull request #148 from alies-dev/modernize/ci-and-tooling

chore: modernize CI, tooling, and test infrastructure

Merge pull request #147 from alies-dev/fix/php84-nullable-deprecation-v2

fix: use explicit nullable types for PHP 8.4 compatibility

Merge pull request #136 from peterdevpl/php8

PHP 8 and PHPUnit 9 support

Merge pull request #134 from xchangeapi/feature/xchangeapicom-support

xChangeApi.com support

Updated Travis config

Making Swap class not final

Merge pull request #121 from florianv/new

Updated the documentation for the new version

Fixed documentation links

Merge pull request #105 from ddinchev/master

Update swap towards latest exchanger version.

Use the latest exchanger version