SmallFileBuffer and BigFileBuffer

Following up on previous comments in the multiprocessing feature request thread.

One of the most common workloads I have, is copy/move files from local disks to network disks - and back. The payload is usually a mix of millions of small files (10-512KB) and thousands of medium to large files (10MB to 100+GB).

Using separate, configurable, buffers for small files could speed up the process greatly.