This implements a subclass of mpi4py.futures.MPIPoolExecutor that supports specifying a callback function, and has a consistent API with the other pool classes in schwimmbad.
Coverage decreased (-4.9%) to 48.5% when pulling b4c216c66a7fa14606a7fc26e2e6a2de8d29943c on async-mpi into ed996238a35272401c692b68ea7efa03286dd978 on master.
This implements a subclass of mpi4py.futures.MPIPoolExecutor that supports specifying a callback function, and has a consistent API with the other pool classes in schwimmbad.
@edwardreed81 this might solve #18