Examples pymodelrunner usgae in an mpi enviroment

Currently there are 3 working examples implemented

• Printing a simple message on every worker (one param, a = # of printed messages)
• MPI_REDUCE calculation (two params, N = multiplier used in calculation, maxprocs = maximal number of workers)
• PyMPDATA_MPI carteisan 2D calculation based on Arabas et al. 2014 (three params, options = PyMPDATA options dictionary, courant field multiplier, output steps = # of time steps to calculate)