Mallocate memory when making source buffers for scenekit sources.
Mallocate memory when making source buffers for scenekit sources.

When we import large models as reported in GH Issue # 56 and # 58,
allocating memory for the buffers on the stack won't work, so we
explicilty allocate it on the heap and free this memory once the
scenekit sources have been generated from these source buffers.

dmsurti/AssimpKit