add api calls to get argc and argv inside an actor

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
rename bsal_actor_size to bsal_actor_nodes

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
implement actor affinity execution

Link: https://github.com/GeneAssembly/biosal/issues/20
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>