* Remove several unused functions in doodad.Drawing (velocity, acceleration,
grounded, etc.) - uix.Actor is where these are actually managed.
* In the JavaScript API, setTimeout() and setInterval() will translate the
milliseconds from wallclock time into a fixed number of game ticks to match
the target frame rate for better deterministic timing.
* Switch from otto to goja for JavaScript engine.
* goja supports many ES6 syntax features like arrow functions,
const/let, for-of with more coming soon.
* Same great features as otto, more modern environment for doodads!
* CLI: fix the `doodad convert` command to share the same Palette when
converting each frame (layer) of a doodad so subsequent layers find
the correct color swatches for serialization.
* Scripting: add timers and intervals to Doodad scripts to allow them to
animate themselves or add delayed callbacks. The timers have the same
API as a web browser: setTimeout(), setInterval(), clearTimeout(),
clearInterval().
* Add support for uix.Actor to change its currently rendered layer in
the level. For example a Button Doodad can set its image to Layer 1
(pressed) when touched by the player, and Trapdoors can cycle through
their layers to animate opening and closing.
* Usage from a Doodad script: Self.ShowLayer(1)
* Default Doodads: added scripts for all Buttons, Doors, Keys and the
Trapdoor to run their various animations when touched (in the case of
Keys, destroy themselves when touched, because there is no player
inventory yet)
