Move the hockey example to a separate repository

[luator]

For actual production use, the users should not integrate their code into this package but rather create an own one, which depends on comprl.
I think it would be good to have a small example package for this and would suggest to create one for the hockey game.

Likewise, the implementation of the hockey game server should maybe also be moved to some other repo. This would allow us to get rid of the hockey dependency, which pulls in quite a lot of further dependencies.