Quantizedmesh vertex normals

Here is a gist that can be dropped into the sandcastle gallery for testing.
https://gist.github.com/abwood/e6b3ab977bc6b286f430
This doc doesn't really explain why someone would want to use `requestVertexNormals` or not.  Instead of describing the implementation, why not describe the effect (i.e. allows terrain normals to be used for lighting purposes).  Do we have anywhere in the doc or an example that would help someone figure out how to find and enable this option?  It might make sense to add an example that uses Natural Earth and turns on this options (explaining why).