4.0.0

Easing v4 is here! 🚀
It reworks the internals for better performance and extensibility. The public API remains the same for typical usage, but Easing is now a struct instead of an enum.

Key changes

• Added spring physics-based easings
• Added piecewiseLinear easing similar to CSS linear()
• Bug fixes and performance improvements
• Expanded docs and unit test coverage