* Add animation support for Doodad actors (Play Mode) into the core
engine, so that the Doodad script can register named animations and
play them without managing all the details themselves.
* Doodad API functions on Self: AddAnimation, PlayAnimation,
StopAnimation, IsAnimating
* CLI: the `doodad convert` command will name each layer after the
filename used as the input image.
* CLI: fix the `doodad convert` command creating duplicate Palette
colors when converting a series of input images into a Doodad.
* 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)
