Fixed bug in AllocatorPimpl::CalculateStats
Fixed bug in AllocatorPimpl::CalculateStats

Also added debug macro D3D12MA_FORCE_RESOURCE_HEAP_TIER.
Fixes #10

GPUOpen-LibrariesAndSDKs/D3D12MemoryAllocator,GPUOpen-LibrariesAndSDKs/D3D12MemoryAllocator,GPUOpen-LibrariesAndSDKs/D3D12MemoryAllocator