Fix for fanstatic 1.0a3 / separate publisher and injector tweens

This series of commits:
- Fixes things to work with the new pluggable injector architecture in fanstatic 1.0a3
- Splits `Tween` into `PublisherTween` and `InjectorTween`
- Various other small cleanups/fixes

Sorry for putting them all in a single pull request.  If you'd like them split up, let me know.