Massive FX rewrite. Full list of changes:

- You can now animate non-px values (em and %, for example)
- You can animate things things that previously broke (like font-size)
- You can now write fx plugins (to add in the ability to animate colors, for example)
- Advanced queueing controls were added (.queue(), .dequeue(), and {queue:false})
- Step was re-tooled to work with the new fx plugin scheme
- Added the ability to do relative animations
- Made it so that you can do simultaneous animations on a single element
- A complete refactoring of jQuery.fx, improving naming, and usability