Updating chunksInUse in Allocate/Deallocate results in performance degradation with each allocation.

[m4drat]

1. Completely remove chunksInUse and build it only when we need it (e.g. inside GC::Collect). This structure can be created in O(N), because we need to iterate over all chunks inside current arena starting from the first one. Note that the complexity is really O(N) even considering the fact that we need O(NlogN) to create a map. This works because we are iterating over chunks in a sorted order. Thus it is possible to provide chunksInUse.end() as a hint for insert method
2. Using binary search find closest deallocated chunk inside chunkTreap. Starting from this chunk iterate in the right direction to find if we have required chunk or not.

Complete #29 before fixing this one