lib: intro the mpi module

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
examples: add a basic usage of mpi

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
examples: add README and example host file to mpi example

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>