* dbus/dbus-message.c: move inline docs into .c file

	* Doxyfile (OUTPUT_DIRECTORY): move output to doc/api
	so all docs are under doc/
	(MAN_EXTENSION): generate man pages. Use extension
	".3dbus" which matches ".3qt" on my system,
	I guess this is OK, I don't know really.
	(FILE_PATTERNS): look for .c files not .h, makes sense
	for plain C I think