Start using the class name for handler services (in the documentation)

[coudenysj]

As introduced in https://symfony.com/blog/new-in-symfony-3-3-optional-class-for-named-services
See https://symfony.com/doc/current/best_practices/business-logic.html#services-naming-and-configuration

[sstok]

Looks good to me 👍

[UFOMelkor]

Thanks @coudenysj for your contribution 👍
Please remove the public attributes. While it's correct that they are currently necessary, the next release will not require them anymore. See #56 for more information.

[coudenysj]

@UFOMelkor Done

[UFOMelkor]

Thank you!