Generate multiple parallelizable SQL files (#839)

Generate multiple SQL files to be imported in parallel.
The files will respect the cross-layer dependencies,
so they can be all ingested at the same time.

docker-compose.yml

@@ -41,7 +41,7 @@ services:
     volumes:
       - .:/tileset
       - ./data:/import
-      - ./build:/sql
+      - ./build/sql:/sql
       - ./build:/mapping
       - ./cache:/cache