Add audience test sample;

examples/example_audience.py

+import jpush as jpush
+from conf import app_key, master_secret
+_jpush = jpush.JPush(app_key, master_secret)
+
+push = _jpush.create_push()
+push.audience = jpush.audience(
+            jpush.tag("tag1", "tag2"),
+            jpush.alias("alias1", "alias2")
+        )
+push.notification = jpush.notification(alert="Hello, world with audience!")
+push.platform = jpush.all_
+push.send()