* The Anvil doodad is affected by gravity and becomes dangerous when
falling. If it lands on the player character, you die! If it lands on
any other mobile doodad, it destroys it! It can land on solid doodads
such as the Electric Trapdoor and the Crumbly Floor. It will activate
a Crumbly Floor if it lands on one, and can activate buttons and
switches that it passes.
* JavaScript API: FailLevel(message) can be called from a doodad to kill
the player character. The Anvil does this if it collides with the
player while it's been falling.
* Add a Level Exit doodad, which for now is a little blue flag on a pole
that reads "END"
* JavaScript API: global function EndLevel() will end the level. The
exit doodad calls this when touched by the player.
* Add a "Level Completed" alert box UI to PlayScene with dynamic button
layouts.
* The alert box pops up when a doodad calls EndLevel() and contains
action buttons what to do next.
* "Play Again" restarts the current level again.
* "Edit Level" if you came from the EditorScene; otherwise this button
is not visible.
* "Next Level" is a to-be-implemented button to advance in the single
player story mode. Only shows up when PlayScene.HasNext=true.
* "Exit to Menu" is always visible and closes out to the MainScene.
