Release a version with -m mpi4py -c 'command' support.

[Former user]

As I am porting old python-mpi scripts to -m mpi4py I realized the upstream release version 2.0.0 doesn't support '-c' syntax. Please consider making a release with better compatibility with standard python.

[Lisandro Dalcin]

mpi4py 3.0.0 just released!