Version 0.3

This is the first major behavior change in nbd:

* `Class` subclasses no longer automatically call their super's `.init()`
* The `_` static property to stop the autocalling behavior has been removed
* MVC classes now default to using `._model` and `._view` to refer to their own instances of models and views. `.Model` and `.View` are still supported, but schedule for removal in v0.4