Remove down-facing, ground-level faces from buildings
- add `preserveGroundFaces` option to `BlueprintOutputBuildingTiles` to keep the faces
- otherwise discard them, for smaller geometry buffers
Merge branch '0.2.0' into remove-ground-faces
Fix down-facing, ground-level building faces check for imprecise floating point values (#102)
Merge branch '0.2.0' into remove-ground-faces

Conflicts:
	src/Blueprint/BlueprintOutputBuildingTiles.js
Merge pull request #102 from brianchirls/remove-ground-faces

Remove down-facing, ground-level faces from buildings