NEW get_event method, get_events -> list_event

You guys have been busy!  I didn't see this one when going through the first
time.

Anyway, Client#get_events has migrated to #list_events, it will gain the new
signature in the next commit.  Client#get_event implements the Events.Get
action described here: http://orchestrate.io/docs/api/?go#events/get18

I believe this is the first client implementation of this :P