Implement animation tweening API powered by Tween.js, Popmotion, or some other lib.

[trusktr]

Popmotion has progressed a lot as an animation library since it came out! It's not just a tweening library anymore. Tween.js is nice, but it's just a tweening library. Popmotion has physics!

Let's add an API that makes it easy to animate Node properties, powered by Popmotion behind the scenes.

Currently, using a tween library directly is much too verbose. For example, see the JavaScript in this animated button demo: https://codepen.io/trusktr/pen/rpegZR

We can eliminate a ton of that boilerplate code by providing a nice animation API. The result will be something that is as simple as working with CSS animations that can be started, stopped, and cleaned up simply by adding and removing classes. In this case, the API will be JavaScript-based, but similar in the sense that you just tell your object what state it should go to, and the stopping and clean up of animations is abstracted behind the scenes.

In CSS, selectors are associated with states. In the future, it might be possible to use CSS custom properties to achieve a custom CSS-based approach.