v4.0.0

What's new:

• Support for PHP 7.3+
• Upgraded Tus library to v2.3
• Upgraded PHPUnit to v9
• Upgraded Psalm to v4.30
• Upgraded php-coveralls to v2.7
• Upgraded PHPUnit test configuration
• Updated namespace from Vimeo to Vimeify/Vimeo
• Dropped Travis
• Dropped Styleci
• Removed useless files (composer.phar, autoload.php)