v19.0.0 - Stop the monkeys!

Breaking change:

• The Easing object is no longer monkey-patchable, i.e. it has been frozen with Object.freeze(). If you relied on patching Easing, instead you should use alternative references for the easing functions you wish to use.

From now on we will also keep the changelog updated with each release so that it is easy to see what changed and if any migration is needed for breaking changes.