Fix some vague things, and add some stuff in preparation for the Snap! plugin. - Fix a bug opening new Scratch 2.0 files - Fix a bug opening projects made with Kurt in Scratch 1.4
API changes: - `Project.thumbnail` is now an `Image`, not a `Costume`. This is a _mostly_ backwards-compatible change.
2.0.0
- All-new interface - Supports both Scratch 1.4 and 2.0 - Documentation hosted on [Read the Docs](http://kurt.readthedocs.org/)