Initial attempt to document events and payloads.

In no way complete - most have been trial and error and some
deducing what they could mean. It needs more information from
someone that knows the code better. But this is a start and
it lays the basic structure for adding this additional detail.

Signed-off-by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Prakash Surya <surya1@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2357

man/man5/Makefile.am

@@ -1,4 +1,4 @@
-dist_man_MANS = vdev_id.conf.5 zpool-features.5 zfs-module-parameters.5
+dist_man_MANS = vdev_id.conf.5 zpool-features.5 zfs-module-parameters.5 zfs-events.5
 
 install-data-local:
 	$(INSTALL) -d -m 0755 "$(DESTDIR)$(mandir)/man5"