Initial changes to simplify billboard texture creation.
Fix TextureAtlas tests.
Update billboard code to match changes.
Allow setting image back to undefined.
Work on fixing tests
Fix tests.
Add ready flag to Billboard, and add more tests.
Update CHANGES
Remove unused modules.
Fix potential race condition when setting an in-flight image to undefined.
Use canvas when drawing points instead of a function.
Inline image/subregion code in constructor so _loadImage only needs to be called once.
Merge pull request #1959 from AnalyticalGraphicsInc/texture-atlas-changes

Texture atlas changes