ENH: Add basis for minute rate emission of performance.

- Create different benchmark containers in performance
  depending on emission rate.
- Add a minute close method which updates algorithm and
  benchmark returns, and calculates the risk metrics
  depending on those methods.
- Provide fake 0.0 values for annualized metrics like
  sharpe, sortino, and information, until we figure out
  how they should be treated in the context of minutely
  calculation.

*NOTE* This does not fully work without the changes to the
simulation loop by @fawce

tests/test_perf_tracking.py

@@ -1047,19 +1047,31 @@ class TestPerformanceTracker(unittest.TestCase):
                                   dt=foo_event_1.dt,
                                   price=10.0,
                                   commission=0.50)
+        benchmark_event_1 = Event({
+            'dt': start_dt,
+            'returns': 1.0,
+            'type': DATASOURCE_TYPE.BENCHMARK
+        })
 
         foo_event_2 = factory.create_trade(
             'foo', 11.0, 20, start_dt + datetime.timedelta(minutes=1))
         bar_event_2 = factory.create_trade(
             'bar', 11.0, 20, start_dt + datetime.timedelta(minutes=1))
+        benchmark_event_2 = Event({
+            'dt': start_dt + datetime.timedelta(minutes=1),
+            'returns': 2.0,
+            'type': DATASOURCE_TYPE.BENCHMARK
+        })
 
         events = [
             foo_event_1,
             order_event_1,
+            benchmark_event_1,
             txn_event_1,
             bar_event_1,
             foo_event_2,
-            bar_event_2
+            benchmark_event_2,
+            bar_event_2,
         ]
 
         messages = {date: snapshot[-1].perf_messages[0] for date, snapshot in