Add `Color.toBytes` to match `Color.fromBytes` (and also to make tests more readable)
Add `Texture.clear`.

Also fill in more documentation, and clean up the code and the specs for Texture.
Fix logo processing.

* make logoOffset work properly
* clear texture before copying in new logo regions
Remove `Texture.clear` and instead just delete and recreate the texture every time it changes.

texImage2D doesn't work reliably with a null source, and apparently I'm crazy for wanting to clear a texture anyway.
Move sampler-related specs to a separate spec.
Fix an off by one error in CZML handling

When CZML packets have overlapping data within the same interval, we were improperly merging them together, resulting in out of order data.  I fixed the issue and added a unit test to cover it.
Merge pull request #509 from AnalyticalGraphicsInc/offByOne

Fix an off by one error in CZML handling
Merge pull request #507 from AnalyticalGraphicsInc/logo-offset

Fix problems with logos
Merge branch 'master' into cesium.agi.com