* Add better support for 3d buildings
Change key from "levels" to "building:levels" as the "levels" key is non-standard and sees much less use than "building:levels"
* Fix typo in sql definition and missing render_min_height
* Add render_height and min_height to building.yaml
* Simplify the render, switch numeric to int.
Assume min_height cannot be negative. There are a few examples in overpass, but can't show below ground anyways in mapbox (https://github.com/mapbox/mapbox-gl-js/issues/3456). Also don't attempt to fix min_height>height
* Remove colour as it is not currently used
