Use C++ MPI interfaces instead of C interfaces.

[PytLab]

Hi,

I tried to change the use of interfaces of MPI from C to C++. It will make the coding style more uniform and helps to remove the dummy arguments like int argc and char** argv etc. :)

Shao Zhengjiang

[leetmaa]

Thanks for the update. It looks really good. I don't have proper MPI testing capabilities at the moment, but as soon as I have I'll test and merge this.