Memory Pool and Bucket Allocator

[Thanduel]

The purpose of this is to review, improve and apply the memory pool implementation that was started here ​http://trac.wildfiregames.com/ticket/2020 for the purpose of improving the performance of 0ad.

At the moment the plan is to simplify this implementation by removing the dynamic pool which I think is unnecessary. We don't really want the pool resizing itself in the middle of the game as it defeats the object of the pool. The pool will fall back on malloc if it has reached it's capacity. This will mean that in the worst case the performance will default back to what it is now. Further, I intend to add some form of logging to this to allow the user to determine how big the pools actually need to be through playing the game.