Pubsub: macros for ease-of-use and typesafety.

src/lib/pubsub/include.am

src/lib/pubsub/pubsub.h

src/lib/pubsub/pubsub_macros.h

src/test/include.am

src/test/test.c

src/test/test.h

src/test/test_pubsub_build.c