Some sketchy code to start adding velocity support.
Ongoing velocity work.
Merge remote-tracking branch 'origin/master' into velocity
Cleanup velocity handling.
Add SampledPositionProperty specs for velocity
Merge remote-tracking branch 'origin/master' into velocity
Added support for Hermite Interpolation of values along with their derivatives.
Merge remote-tracking branch 'cesium-OpenSource/velocity' into velocity
Added specs for the derivative Hermite interpolation and fixed a couple minor bugs.
Merge remote-tracking branch 'origin/master' into velocity

Conflicts:
	Source/DynamicScene/SampledPositionProperty.js
Adding myself to the contributors list.
Fixing the errors Matt pointed out in his review, mostly Doc related.
Merge remote-tracking branch 'origin/master' into velocity
Merge remote-tracking branch 'cesium-OpenSource/velocity' into velocity

Conflicts:
	Source/Core/HermitePolynomialApproximation.js
Removing unnecessary "argument required" error tags in doc.
cartesian 2
cartesian 4
Cartesian3, except CameraFlightPath
Fixing copy/paste error in error check.
Small edits to wording of error messages and their documentation.