addded initial version of WallGeometry
added WallGeometry sandcastle demo
code clarifications for WallGeometry
Merge remote-tracking branch 'upstream/batching' into batching
added WallGeometry comment into CHANGES.md
added PolygonGeometry
updated WallGeometry to expect positions in Cartesian instead of
Cartographic
Rename ExtentTessellator to ExtentGeometry.
Remove unused code.
Change ExtentTessellator to be ExtentGeometry (computes positions only).
Add texture coordinates to extent geometry.
Add normal, tangent, and binormal vertex attributes to extent geometry.
Remove 'configureExtent' from Polygon. Revert CesiumViewer.
Update doc and tests for extent geometry.
Compute bounding sphere of an extent at a height above the surface.
Update CHANGES.md.
Throw exception when extent is not given. Add test.
added BaseLayerPicker capability to receive an array of providers
and to accept ImageLayers as well as providers
added destroy function to Timeline
initial implementation
working implementation with some tests
allocation cleanup and exception tests