* New Doodad: Checkpoint Flag. They update the player's spawn point
whenever the player passes one. The most recently activated
checkpoint is rendered brighter than the others.
* End Level Modal: the fake alert box window drawn by the Play Mode
is replaced with a fancy modal widget (similar to Alert and Confirm).
It handles level victory or failure conditions and can show or hide
all the buttons as needed.
* Gameplay: There is a "Retry from Checkpoint" option added, which
appears in the level failure modal. It will teleport you back to
the Start Flag or the last Checkpoint Flag you had touched, without
resetting the level -- your keys, unlocked doors, etc. will be
preserved so you can retry.
* Set a maximum speed on the "Camera Follows Actor" logic of 64
pixels per tick. This results in a smoother scrolling transition
when the player jumps to a new location on the map, such as by
a Warp Door.
* Update the default color palettes:
* All: Add a "hint" magenta color.
* Colored Pencil: Add a "darkstone" solid color.
Updates to the Doodads JavaScript API:
* SetCheckpoint(Point(x, y)): set the player character's spawn
position. Giving it Self.Position() is an easy way to set the
player spawn to your doodad's location.
