core: use memory fence on x86 too

Link: https://github.com/GeneAssembly/biosal/issues/744
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
documentation: update concepts table in readme

Link: https://github.com/GeneAssembly/biosal/issues/745
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: use a threshold lower than the ideal size

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: the suggested buffer size is now available in the API

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: increase maximum number of active messages

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: move thorium_worker_print_actors in worker_debugger

Link: https://github.com/GeneAssembly/biosal/issues/672
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>