Fixes #1057 This PR adds `amenity=grave_yard` to the `landuse` layer. A unification function was implemented which encodes all `class=grave_yard` as `class=cemetery` in the tiles, which adds these features for existing users of `class=cemetery` with no change. The unification function can serve as a basis for any other tags that we might want to unify in the `landuse` layer. Tile rendering for an `amenity=grave_yard`. ([Location](https://www.openstreetmap.org/way/857383420))  Tile rendering for a `landuse=cemetery`. ([Location](https://www.openstreetmap.org/way/385779531)) 
landuse
Docs
Read the layer documentation at http://openmaptiles.org/schema#landuse

