Modify mpi.py to facilitate sending control messsages back from workers to master.
Add memoized property decorator.
Add method to mpi.Manager to process ctrl messages from workers, add memoized rank property to mpi.Worker.
Add memoized MPI size attrib to Worker and Manager, move max_steps validator from base.py to mpi.py.
Send timing data collected from workers to master.
Add preliminary code to base.Manager to compute average received data throughput.