In the Doodad Properties window, instead of browsing to select a .js
file to install your script, a SelectBox of built-in generic scripts are
available. These scripts implement simple behaviors and adapt to the
full canvas size of the doodad.
Built-in scripts so far include:
* generic-anvil.js: behaves just like the Anvil.
* generic-fire.js: the entire canvas hitbox acts like fire pixels,
"burning" mobile doodads and failing the level for the player.
* generic-solid.js: the entire canvas hitbox acts solid
