PHP file throws PHP Fatal error: Class 'Zend\Serializer\AdapterPluginManager' not found

Somehow the Zend dependencies does not seem to be correct, that's why the PHP file throws this fatal error after doing composer install and calling
php -f namespacer.php

This can e.g. be solved by replacing all Zend Framework packages by
"zendframework/zendframework": "2.3.*"
in the composer.json file.

[dmnc]

It becomes a little more complex than that because which packages require which has changed over time. #6 fixes this though.