old values in the update event

[mkabilov]

in case of update events sometimes it's useful to know which row is updated.
currently only new values will be stored in the event struct:

psql-streamer/source/postgres/postgres.go

Lines 321 to 324 in 27c70ce

	case pgoutput.Insert:
	ev, err = s.generateEvent(event.ActionInsert, v.RelationID, v.Row)
	case pgoutput.Update:
	ev, err = s.generateEvent(event.ActionUpdate, v.RelationID, v.Row)

[blind-oracle]

Hi. Will think about it :)