* Refactor the events used in lib/render/sdl to be more general-purpose to make librender a stand-alone library separate from Doodle.
* On the Doodads tab is the Link button to enter the Link Tool. * Click Link, then click the 1st doodad on the level, then click the 2nd doodad to complete the link. * The actors struct in the Level holds the link IDs for each actor.
* All private Doodle source code into the pkg/ folder. * Potentially public code into the lib/ folder. * Centralize the logger into a subpackage.
