Added acknowledgements, required by some third-party libraries#1628

Merged

tobbi merged 3 commits intoSuperTux:masterfrom

Semphriss:acknowledgements

Jan 24, 2021

Commits on Dec 30, 2020

Added acknowledgements, required by some third-party libraries
Semphris
committed
Fixed Boost code quality error
Semphris
committed

Commits on Jan 10, 2021

Added missing BOOST library for acknowledgements
Semphris
committed