context.events should use dot notation

Ideally we'd be able to do something like this:

``` python
event_names = [event.action.name for event in events]
if 'Approve Taxes' in event_names and 'Approve Parking' in event_names:
change_state('Approved')
```

But currently we have to use:

``` python
event_names = [event['action']['name'] for event in events]
```

Not a huge deal, just easier to write.
Related to #20

未指定文件、测试或入口点。首先追踪 context.events 的构造和使用方式，然后找出现有的事件访问测试；支持所示的点号表示法示例，同时不破坏当前的字典式访问，即视为完成。

由索引模型根据 Issue 内容生成。