Use AsteroidPools class and begin to migrate pools to it
Use AsteroidMedium through AsteroidPools
Use AsteroidSmallPool through AsteroidPools
Use AsteroidPolls in each Asteroid subclass
Remove LargeFactory
Remove MediumFactory
Remove SmallFactory
remove ConcretePool for a while
simplify LargePool
simplify MediumPool
simplify SmallPool
remove LargePool
remove MediumPool
remove SmallPool
remove abstract Pool
remove Large
remove Medium
remove Small