Making this change will mean that the category used to configure loggin will also need to change.  Previously, the following would work:

```
  <category name="p6spy">
    <priority value="DEBUG" />
  </category>
```

With this change it would become

```
  <category name="com.p6spy.engine.spy.appender.Slf4JLogger">
    <priority value="DEBUG" />
  </category>
```
or a parent package like `com.p6spy`.

While this is not a terribly bad thing, it does give users the impression that they could configure logging for p6spy.  Unfortunately, this would not be the case as we only use a single logger.