Make Dat._data temporarily writable for halo exchange
Add MPI advection-diffusion demo
Add output testing for MPI advection-diffusion demo
Add profiling option for MPI advection-diffusion demo
Add error checking and profiling options to sequential adv-diff demo
Add advection-diffusion sequential regression test
Add decomposed meshes for MPI advection-diffusion demo
Add MPI advection-diffusion regression test
Only print error if --print-output is given