Updated b21 in CHANGES.md
Update version in build.xml to b21
Initial commit for issue #1076.  Added translucencyByDistance to billboard
and incorporated into Label.  SandCastle examples added for both label and
billboard fading based on camera distance.

Signed-off-by: Alex Wood <abwood@gmail.com>
Merge remote-tracking branch 'agi/master' into issue1076
Fixed typo in Billboard asset name.

Signed-off-by: Alex Wood <abwood@gmail.com>
Fixed bug that would occur if some billboards in a collection did not use
scale/translucencyByDistance, their default values would cause issues.
For translucency and scale, we should default to 1.0 which results in an
identity transformation (e.g., scale by 1).

Signed-off-by: Alex Wood <abwood@gmail.com>
Added unit tests for Billboard.translucencyByDistance and
Label.translucencyByDistance.  Cleanup and fixes related to unit tests.

Signed-off-by: Alex Wood <abwood@gmail.com>
Added unit tests for picking labels and billboards that use
translucencyByDistance.  Picking fixes for translucencyByDistance.  Updated
Changes.MD.

Signed-off-by: Alex Wood <abwood@gmail.com>
Minor documentation fixes.

Signed-off-by: Alex Wood <abwood@gmail.com>
Make sure we create a default billboard.