Zif v2.3.1: Fix one-off animations & callbacks

Tested against DRGTK 5.5 & Smaug config updated

This release includes a fix for reusing one-off animations & using callbacks at the end of an action which cause another action to be added.

An example is included in the example app: when the button is pressed, the dragon will flap its wings slowly for a moment, before going back to the normal flapping animation.

What's Changed

• Fix one-off animations & Allow animation callbacks to run an animation sequence by @danhealy in #39

Full Changelog: v2.3.0...v2.3.1