Add Debug Mode that prints internal statuses at run time.

A way for end users to observe behavior trees in action.

Allow for setting at root of a tree and that value gets passed down the tree. IE:

```
Sequence(
    Decorator(
        Action()
    ),
    debug=True
)
```

Should activate debug mode for all three objects.

Also allow debug mode at run time via debug keyword argument to `__call__`.