man: add missing references to sd_event_add_inotify()

man: add missing references to sd_event_add_inotify()

These man pages list references to the various sd_event_add_xyz() calls
at the bottom, but sd_event_add_inotify() was never added there.

Moreover, some list references to sd_event_add_post() and
sd_event_add_exit() even though these have shared man pages with
sd_event_add_defer(), and given that the "SEE ALSO" section should
probably reference pages instead of functions let's drop this.

Then, let's always specify the sd_event_add_xyz() calls in the same
order.

Finally, in the sd_event_new(3) text explaining the basic logic,
actually mention sd_event_add_post() and sd_event_add_exit() as well, as
in that case we actually want to list functions, not man pages.