[OSM-dev] OpenStreetMap Carto schema change updates

[Paul Norman]

We've decided to drop support for old-style multipolygons in 
OpenStreetMap Carto 4.0.0. This has resolved our outstanding issues, and 
we now feel the work is ready to merge. The big changes are

- database schema change;

- disjoint area handling;

- different tag columns; and

- multipolygon handling changes

Issues should be raised at 
https://github.com/gravitystorm/openstreetmap-carto/pull/2533