highlight places where code is needed with "TODO"

Link: https://github.com/GeneAssembly/biosal/issues/1
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
remove unused functions

Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
restore vtable code for bsal_actor

Link: https://github.com/GeneAssembly/biosal/issues/5
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>