Generate new platforms as you climb.

This is actually broken as platforms never unregister themselves. An upcoming
refactoring will change things, so registering/unregistering will not be
necessary anymore.

src/platformsystem.hpp

@@ -52,6 +52,7 @@ namespace cloonel {
 		const std::unique_ptr<LocalData> m_localdata;
 		ColliderRegisterFunc m_registerToCollider;
 		ColliderUnregisterFunc m_unregisterFromCollider;
+		float m_targetAverage;
 	};
 } //namespace cloonel