add authorship of David Maul

src/game/core/Engine.cpp

src/game/core/Engine.hpp

src/game/core/Scene.hpp

src/game/core/Spritesheet.cpp

src/game/core/Spritesheet.hpp

src/game/core/Tile.cpp

src/game/core/Tile.hpp

src/game/core/Window.cpp

src/game/core/Window.hpp

src/game/effect/Effect.cpp

src/game/effect/Effect.hpp

src/game/level/Level.cpp

src/game/main.cpp