Hello world

# examples/01-hello.jl
using MPI
MPI.Init()

comm = MPI.COMM_WORLD
print("Hello world, I am rank $(MPI.Comm_rank(comm)) of $(MPI.Comm_size(comm))\n")
MPI.Barrier(comm)

> mpiexecjl -n 4 julia examples/01-hello.jl
Hello world, I am rank 1 of 4
Hello world, I am rank 2 of 4
Hello world, I am rank 0 of 4
Hello world, I am rank 3 of 4