ENH: Add style parameters to order API helper methods.

Add `style` parameter to order_value, order_percent, order_target,
order_target_percent, and order_target_value methods.  The style parameter is
forwarded to the underlying call to `order`.

tests/test_algorithm.py

@@ -26,6 +26,7 @@ import zipline.utils.simfactory as simfactory
 from zipline.test_algorithms import (TestRegisterTransformAlgorithm,
                                      RecordAlgorithm,
                                      TestOrderAlgorithm,
+                                     TestOrderStyleForwardingAlgorithm,
                                      TestOrderInstantAlgorithm,
                                      TestOrderValueAlgorithm,
                                      TestTargetAlgorithm,
@@ -211,6 +212,24 @@ class TestTransformAlgorithm(TestCase):
             )
             algo.run(self.df)
 
+    def test_order_method_style_forwarding(self):
+
+        method_names_to_test = ['order',
+                                'order_value',
+                                'order_percent',
+                                'order_target',
+                                'order_target_percent',
+                                'order_target_value']
+
+        for name in method_names_to_test:
+            algo = TestOrderStyleForwardingAlgorithm(
+                sim_params=self.sim_params,
+                data_frequency='daily',
+                instant_fill=False,
+                method_name=name
+            )
+            algo.run(self.df)
+
     def test_order_instant(self):
         algo = TestOrderInstantAlgorithm(sim_params=self.sim_params,
                                          data_frequency='daily',