fix types

[Xuleos]

puts the types for useSprings, useTrail, and useSpring all in a usable state.

also makes it so that configs and easings are exported from index.d.ts so that the imports get compiled correctly

[chriscerie]

Thanks! It looks like for imperative api, styles doesn't include spring keys that are in to and falsely includes reserved props. Can we try to fix this? We can also merge this for now and open an issue to revisit later.

// Expected - styles: { x: Roact.Binding<number> }
// Actual - styles: { to: Roact.Binding<{ x: number }> }
const [styles, api] = useSpring(hooks, () => {
  return { 
    to: { x: 3 },
  };
});

[chriscerie]

Finally got around to reviewing this longer than I should have. Validated compatibility with recent changes, will open an issue to track comment above. Thanks! 🎉