Uses dictionary update instead of iterating through keys.

update_universe is a bottleneck on large data sets.

A large portion of that bottleneck is the call to getitem while
looping over the keys, so using update while passing along the internal
__dict__

Seeing about a 40% improvement.

zipline/gens/tradesimulation.py

@@ -241,8 +241,7 @@ class AlgorithmSimulator(object):
         self.algo.set_portfolio(event.portfolio)
 
         # Update our knowledge of this event's sid
-        for field in event.keys():
-            self.universe[event.sid][field] = event[field]
+        self.universe[event.sid].update(event.__dict__)
 
     def simulate_snapshot(self, date):
         """