Adding LayerBoundary
Renamed LayerState => LayerBuilder. Rewritten, with modifications to LayerStrategy for support (passing pointers now instead of trails, to remove more internal state)
Renaming layerState => layerBuilder in LayerStrategy
Removing TODO note
Scene / Layer handling for boundaries. Removed 'entry' parameter, added startBoundary / endBoundary in parameter object.
Updating debugging test
Boundary hasPrevious/hasNext switched to self trail instead of layer type, since we were using switchToLayer at the exit().
Improving layering unit test, since it spit out megabytes of info on test failures
Trail.compare note
layerLookup changed to use selfTrail comparison
Adding boundaries reference + debugging output
Fixed missing trail copy()
Removing trailing whitespace, commenting out debugging information for now
Fixing performance regression by including too much in Scene.affectedLayers()