This renames e.g. struct bus_body_part -> BusMessageBodyPart to
follow our usual coding style. Also, several struct and enum
declarations are moved to relevant headers.
Also, this introduces bus-forward.h.
Now that the necessary functions from log.h have been moved to macro.h,
we can stop including log.h in macro.h. This requires modifying source
files all over the tree to include log.h instead.
Yu Watanabe
Daan De Meyer
Jan Janssen
Lennart Poettering