Static Geometry Batching

We started work on new geometry types (think extruded volumes, cylinders, walls, etc.) and the ability to batch them together into a single primitive for high-performance when drawing a lot of static geometries.

Besides being required for KML, this will make writing custom rendering code much easier, since, in most cases, users just want to define new geometries, not do actual rendering.

The details are on the roadmap: #766

Feedback and pull requests are welcome.