Copied drawer.js to tiledImage.js
Splitting drawer into drawer/tileCache/tiledImage; adding World
Merge branch 'collections' into ian
Merge branch 'collections' into ian

fixed Conflicts:
	src/drawer.js
Deprecated layer functions in viewer; additional cleanup.
Cleaned up tileCache code.
Further cleanup
World.getHomeBounds()
Previous cleanup was a little too aggressive.
Moved Viewport.goHome to Viewer.goHome.
Merge branch 'collections' into ian
Fixed home/constraints for multi-image.
Unit test fixes.
World cleanup; viewer layer function deprecation
Converted layer tests to multi-image tests
Renamed layers.js to multi-image.js
More test fixes.
Moved update-viewport event
Reinstating a small check.
Merge pull request #450 from openseadragon/ian

WIP: Splitting drawer into drawer/tileCache/tiledImage; adding World