Note that we have a higher-than-normal score by default. This makes it easy to program two common cases for conversational states. First, the more common case, where you want a single message for both implied and explicit greetings: just create a HelloTopic, since that responds to both kinds. Second, the less common case, where we want to differentiate, writing separate responses for implied and explicit greetings: create a HelloTopic for the explicit kind, and ALSO create an ImpHelloTopic for the implied kind. Since the ImpHelloTopic has a higher score, it'll overshadow the HelloTopic object when it matches an implied greeting; but since ImpHelloTopic doesn't match an explicit greeting, we'll fall back on the HelloTopic for that.
ImpHelloTopic : MiscTopic